Comparing different methods of analysing sewage sludge, dewatered sewage sludge and sewage sludge ash

The following article compares different ways of characterising sewage sludge. Against the background of sludge recycling in agriculture as well as treatment with subsequent phosphorus recovery in mind, the article starts by collating and evaluating the levels of phosphorus, heavy metals, chlorine and sulphur in sludge as reported in the literature. Sewage sludge from the sewage treatment plant at Kaditz in Dresden was analysed using standardised and adjusted methods, which produced different results. In the course of this analysis the results were produced by using elemental analysis, atomic absorption spectroscopy, X-ray fluorescence spectroscopy (X-RFA) and ion chromatography (IC). The second part of the article therefore seeks reasons for the differences in the findings and tries to give solution statements. The article closes by calculating transfer coefficients for selected parameters during the incineration process and solid-liquid separation and weighing up the analysis techniques compared. Basically this article will show significant differences in sludge composition and the effects on the specific elements by ashing or mechanical dewatering of the different sludges. An essential attention obtains the analysis by using the X-RFA.     

Influence of treated sewage sludge applications on temporal variations of plant nutrients and heavy metals in a Typic Xerofluvent soil

The objective of this study is to determine influence of Treated Sewage Sludge (TSS) rates as organic matter and nutrient resource on temporal variations of some macronutrients and micronutrients and heavy metals concentrations in a Typic Xerofluvent soil. The experiment was conducted in Menemen Plain, in the Western Anatolia Region of Turkey in 2003–2005. Moist TSS was added to the soil at the rates of 0, 30, 60 and 90 Mg ha⁻¹ on May 1, 2003. Peanut (Arachis hypogaea) was planted as the first crop. On the other hand, mixture of green barley (Hordeum vulgare) and common vetch (Vicia sativa L.) was planted as the second crop. During the experiment, soil samples were taken five times. Increasing TSS applications to this soil resulted in significantly increased concentrations of total N, Cu, Pb and Ni, and available P, K, Ca, Fe, Cu, Zn, Mn concentrations in soil. However, concentrations of available Mg and Na, total Fe, Zn, Mn, Cd, Co and Cr in soil did not significantly change. Micronutrients and heavy metals concentrations in soil were found under threshold values in all sampling periods in this study. Available nutrient concentrations in the soil decreased particularly in the last sampling periods because of plant uptake of nutrients from the applied TSS. It is recommended that 90 Mg ha⁻¹ moist TSS can be added once in a 2-year period for improving nutrient concentrations in Typic Xerofluvent soil.     

Ammonium nitrogen uptake by rice grown in acid sulfate soil under controlled redox conditions

A study was conducted to determine plant growth and ammonium fertilizer nitrogen uptake by rice (Oryza sativa, L.) in acid sulfate soils (Sulfic Tropaquept) as affected by soil redox conditions. Rice seedlings of acid sulfate soil-tolerant and sensitive varieties (IR 46 and IR 26, respectively) were grown in laboratory microcosms for 3 weeks in soil suspensions incubated at four separate Eh levels (+500, +250, +50, and-150 mV). Growth of both varieties decreased as soil Eh decreased. Uptake of both added¹⁵N labelled (NH₄)₂SO₄ and native soil nitrogen also decreased with decreasing soil Eh. Percent N from fertilizer in the plant tissues increased with decreasing soil Eh. Nitrogen uptake was greater in IR 46 as compared to IR 26. A greater amount of fertilizer N and native soil N remained in the soil suspension under a highly reduced condition compared to an oxidized condition indicating that more ammonium N was utilized by the rice plants under the oxidized than the highly reduced conditions. The growth of the soil tolerant rice variety (IR 46) was more superior to that of the sensitive rice variety (IR 26) under oxidized (+500 mV) and moderately reduced (+250 to +50 mV) than highly reduced (-150 mV) conditions. Greater uptake of soil and fertilizer nitrogen was measured under the soil redox conditions in which adequate plant growth was recorded. Strongly reducing soil redox conditions adversely affected plant growth which in turn limited nitrogen uptake.     

磷酸活化法制备污泥含碳吸附材料的研究

研究了磷酸活化法制备污泥含碳吸附剂的工艺条件,探讨了活化剂质量分数、活化温度、活化时间和浸渍质量比对活化效果的影响.结果表明,在磷酸质量分数为50%、活化温度450℃、活化时间1 h、浸渍质量比1.5:1的条件下,制得的含碳吸附剂碘值在210 mg/g以上,产品收率50%,应用该吸附材料处理废水效果较好.     

An experimental study of oil recovery from sewage sludge by low-temperature pyrolysis in a fluidised-bed

Pyrolysis of activated sewage sludge was investigated under inert conditions in a fluidised-bed to study the effects of temperature and gas residence time on the product distribution and composition with an aim to maximise the oil yield. The temperature was varied from 300 to 600 °C and the gas residence time from 1.5 to 3.5 s. Three groups of products were produced, namely, a non-condensable gas (NCG) phase, a solid phase (char) and a liquid phase (oil). A maximum of 30% oil yield (wt% daf of sludge fed) was achieved at a pyrolysis temperature of 525 °C and a gas residence time of 1.5 s. Higher temperatures and longer gas residence times favoured the formation of NCG, suggesting that secondary cracking reactions had occurred. The oil obtained was analysed using GC-MS and H NMR to determine the oil's composition and structure, a unit structure of the oil was proposed which consisted of aromatic rings connected by hydrocarbons with -OH functional groups attached.     

Benefits of organic residues and chemical fertilizer to productivity of rain-fed lowland rice and to soil nutrient balances

Low yields and high risk characterize many rain-fed lowland rice environments, including those in Laos. Drought and fluctuating soil-water conditions (from aerobic to anaerobic states) can limit productivity and the efficient use of applied nutrients. Although addition of organic matter may improve the efficiency of fertilizer use, on-farm residues, for example farmyard manure (FYM), rice straw and rice hulls, are, currently, poorly utilized in these systems. Single and multi-year experiments were designed to evaluate the effect of these residues on rice productivity and efficiency of fertilizer use at four sites. Rice yield without fertilizer but with addition of residues ranged from 1.1 to 1.7 t ha⁻¹ across sites and years. In response to fertilizer, yields increased on average by 1.4 t ha⁻¹. For all sites and years there was a significant response of yield to organic residues applied without fertilizer, with responses ranging from 0.2 to 1.4 t ha⁻¹. In 58% of cases there was no residue×fertilizer interaction (benefits of residues when applied with fertilizer were additive). In 38 and 4% of cases the interaction was negative (no response to residues if fertilizer was already applied) or positive (synergistic), respectively. In the multi-year studies, the type of interaction varied between years, suggesting that seasonal events, rather than soil type, determine the type of interaction. The greatest benefits of applying organic and chemical fertilizers together were observed in years when soil-water conditions were unfavorable (fluctuating anaerobic–aerobic conditions). The long-term effects of these different management strategies on soil nutrient balances suggest that N, P, and K balances were maintained as a result of balanced commercial fertilizer management but that addition of residues further enhanced these balances. All residues, when applied alone, resulted in positive soil Si balances; only with FYM were long-term N, P, and K balances maintained or positive, however. For resource-poor farmers, applying on-farm residues can be a sustainable approach to increasing productivity.     

城市污泥中重金属去除技术研究

重金属污染是目前城市污水处理厂污泥农用的主要障碍之一。综述了城市污泥中重金属去除的常用四种技术：化学浸提、生物淋滤、动电技术和固化-稳定化,同时分析了污泥中重金属去除技术的发展方向。     

Measurement and simulation of the contact drying of sewage sludge in a Nara-type paddle dryer

Contact drying experiments were carried out in a Nara-type paddle dryer to study the drying kinetics of sewage sludge in the presence of air. In order to have a better understanding of the sewage sludge drying mechanism, a penetration model developed by Tsotsas and Schlünder is used to simulate the drying kinetics of the pasty, lumpy and granular phase which the sludge experiences during the drying process. The pasty phase is assumed to be a saturated particulate phase, and the granular phase is considered as a mono-dispersed particulate phase whose diameter was experimentally determined. In the lumpy phase, a sludge wall sticking still to the paddle-shaft surface was formed, and the heat transfer resistance from the sludge wall is considered during the model calculation. The influence of the drying parameters (temperature, stirrer speed and air flowrate) on the drying process is investigated experimentally and theoretically. The result indicates that the penetration theory is able to describe the sludge drying kinetics of the three distinct phases. Experimental and calculated drying kinetics are in satisfactory agreement for different drying parameters.     

Effect of sewage sludge mix ratio on the biodegradation of diesel-oil in a contaminated soil composting

The objective of this research was an evaluation of amendments for supplementing organic matter for composting of diesel-contaminated soil. The materials used for this study were soil and sewage sludge, which was added as amendments for supplementing organic matter. The ratios of contaminated soil to these materials were 1: 0.1, 1: 0.3, 1: 0.5, and 1: 1 as wet weight basis. Experiments with only additives were carried out as control, and biocide control experiments were also tested by the addition of HgCl². Degradation of diesel was affected by the sewage sludge mix ratio, and the most rapid degradation of TPH was observed in the mix ratios of 1:0.3 and 1:0.5 of contaminated soil to sewage sludge. However, excess addition of these materials did not necessarily facilitate degradation rate. Appropriate mix ratio for effective degradation was 1: 0.5 as a wet weight, and 98.1% of TPH was degraded during the composting period. In biocide control experiments, 8.3% of TPH removal of diesel oil occurred, while 95.3% of TPH was removed in experiment without adding biocide. This indicated inactivation of microbial activity for degrading diesel oil was not completely occurring although significant suppress of microbial activity was observed. Carbon dioxide evolution rate and dehydrogenase activity were matched with the degradation of diesel oil well.     

Technological and environmental behavior of sewage sludge ash (SSA) in cement-based materials

Sewage sludge ash (SSA) is a waste material obtained from the incineration of wastewater sludge. The physical, chemical and mineralogical characteristics of SSA, and the evaluation of its use in cement-based materials, are presented in this paper. Results show that SSA is composed of irregular grains having a high specific surface area and thus leading to a significantly high water demand. A fraction of the ash is rapidly soluble (sulfates, aluminum and silica) and can create new-formed products in presence of lime. SSA induces short delays of cement hydration, probably due to both minor elements of the ash and dilution effect. Compressive strengths of mortars containing 25% and 50% of SSA are always lower than those of reference mortars but it is shown that SSA has a long-term positive effect which might be related to a slight pozzolanic activity. The amount of elements leached from SSA mortars is slightly higher than from the reference mortar without residue but it remains of the same order of magnitude. An extensive literature review was performed in order to compare the residue used in this study with others included in the same category. This analysis highlighted the principal characteristics that must be taken into account to use SSA correctly in cement-based materials.     

Air-steam gasification of sewage sludge in a bubbling bed reactor: Effect of alumina as a primary catalyst

Numerous references can be found in scientific literature regarding biomass gasification. However, there are few works related to sludge gasification. A study of sewage sludge gasification process in a bubbling fluidised bed gasifier on a laboratory scale is here reported. The aim was to find the optimum conditions for reducing the production of tars and gain more information on the influx of different operating variables in the products resulting from the gasification of this waste. The variables studied were the equivalence ratio (ER), the steam-biomass ratio (SB) and temperature. Specifically, the ER was varied from 0.2 to 0.4, the SB from 0 to 1 and the temperature from 750 °C (1023 K) to 850 °C (1123 K). Although it was observed that tar production could be considerably reduced (up to 72%) by optimising the gasification conditions, the effect of using alumina (aluminium oxide, of proven efficacy in destroying the tar produced in biomass gasification) as primary catalyst in air and air-steam mixture tests was also verified. The results show that by adding small quantities of alumina to the bed (10% by weight of fed sludge) considerable reductions in tar production can be obtained (up to 42%) improving, at the same time, the lower heating value (LHV) of the gas and carbon conversion.     

促释型硼泥的养分释放特点及其肥效研究

采用连续浸提、盆栽试验的方法,研究促释型硼泥的养分释放特点及其肥效.连续浸提结果表明,与硼泥相比,促释型硼泥每次的水溶性镁释放量都有提高;烟草盆栽试验结果表明,与硼泥处理相比,促释型硼泥处理烟草的叶绿素含量、光合速率、生物量和镁肥利用率均更优.     

Thermodynamic behaviors of Cu in interaction with chlorine,sulfur, phosphorus and minerals during sewage sludge co-incineration

Thermodynamic equilibrium calculations were performed to reveal effects of interactions among Cl, S, P and other minerals on Cu migration. Our results showed that HCl(g), SO₂(g) and (P₂O₅)₂(g) were released from the sewage sludge co-incineration. Cl was found to weaken adsorption of Cu by Al₂O₃, CaO and Fe₂O₃, while S delayed reactions of Fe₂O₃ and Al₂O₃ with Cu, with P having no effect on reactions between the minerals and Cu. Among the coupled systems of Cl, S and P, the co-existences of Cl and S, and Cl, S and P were determined to inhibit Cu volatilization, and the co-existence of Cl and P had an enhancing effect. Cu migration was affected only by S in the S and P system. With the SiO₂, CaO and Al₂O₃ system, both Cl alone and Cl and P led to failed reactions between the minerals and Cu. In the systems of S, S and Cl, S and P, and S, Cl and P, the migration behavior of Cu was mainly affected by S at low temperatures and by Cl at high temperatures, whereas P had no effect on Cu migration during the entire process.     

Production of ketones from sewage sludge over zirconia-supporting iron oxide catalysts in a steam atmosphere

Recovering useful hydrocarbons from sewage sludge using zirconia-supporting iron oxide catalysts was investigated. Zirconia has activity for decomposing water molecules to generate active oxygen and hydrogen species. These oxygen species spill over to the surface of iron oxide and react with hydrocarbons to produce oxygen-containing organic chemicals such as acetone. Thus, zirconia-supporting iron oxide catalyst has two kinds of active sites on zirconia and on iron oxide. Sewage sludge was hydrothermally liquefied at 573 K in advance, yielding black water containing various hydrocarbons, to enhance the contact of reactant molecules with the catalysts. It was found that the hydrocarbons in the black water converted well to a mixture containing primarily acetone without any carbonaceous residue over zirconia-supporting iron oxide catalysts under the conditions of one atmospheric pressure and superheating steam atmosphere. Furthermore, it was confirmed that acetone was produced continuously from the sewage-derived black water over the catalysts using a bench scale flow reactor.     

Nitrogen-15 balances and nitrogen fertilizer use efficiency in upland rice

Field experiments were conducted in the 1984 and 1985 wet seasons to determine the effect of N fertilizer application method on¹⁵N balances and yield for upland rice (Oryza sativa L.) on an Udic Arguistoll in the Philippines. The test cultivars were IR43 and UPLRi-5 in 1984 and IR43 in 1985. Unrecovered¹⁵N in¹⁵N balances for 70 kg applied urea-N ha^–1, which represented N fertilizer losses as gases and movement below 0.5 m soil depth, ranged from 11–58% of the applied N. It was lowest (11–13%) for urea split applied at 30 days after seeding (DS) and at panicle initiation (PI), and highest (27–58%) for treatments receiving basal urea in the seed furrows. In all treatments with basal-applied urea, most N losses occurred before 50 DS.Heavy rainfall in 1985 before rice emergence resulted in large losses of native soil N and fertilizer N by leaching and possibly by denitrification. During the week of seeding, when rainfall was 492 mm, 91 kg nitrate-N ha^–1 disappeared from the 0.3-m soil layer in unfertilized plots. Although rainfall following the basal N application was less in 1984 than in 1985, the losses from basal applied urea-N were comparable in the two years. Daily rainfall of 20–25 mm on 3 of the 6 days following basal N application in 1984 may have created a moist soil environment favorable for ammonia volatilization.In both years, highest grain yield was obtained for urea split-applied at 30 DS and at PI. Delayed rather than basal application of N reduced losses of fertilizer N and minimized uptake of fertilizer N by weeds.     

Behaviour of dolomite, olivine and alumina as primary catalysts in air-steam gasification of sewage sludge

Sewage sludge gasification assays were performed in an atmospheric fluidised bed reactor using air and air-steam mixtures as the gasifying agents. Dolomite, olivine and alumina are three well known tar removal catalysts used in biomass gasification processing. However, little information is available regarding their performance in sewage sludge gasification. The aim of the current study was to learn about the influence of these three catalysts in the product distribution and tar production during sewage sludge gasification. To this end, a set of assays was performed in which the temperature (750-850 °C), the in-bed catalyst content (0, 10 and 15 wt.%) and the steam-biomass ratio (SB) in the range of 0-1 were varied with a constant equivalence ratio (ER) of 0.3. The results were compared to the results from gasification without a catalyst. We show that dolomite has the highest activity in tar elimination, followed by alumina and olivine. In addition to improving tar removal, the presence of water vapour and the catalysts increased the content of H₂ in the gases by nearly 60%.     

Characterization of tar content in the syngas produced in a downdraft type fixed bed gasification system from dried sewage sludge

Tar yields in the syngas produced in a pilot-scale downdraft type fixed bed gasification system from dried sewage sludge have been quantified and characterized to identify the effect of equivalence ratio (ER of 0.29-0.36). The increase of ER resulted in higher temperature of oxidation zone because air promoted the combustion reaction. High ER and high temperature also enhanced cracking and combustion of tar. Lower tar mass was observed while increasing ER. The change in tar composition with the change of ER was also observed by using the size exclusion chromatography (SEC). The SEC results showed that heavier molecular tar (in the molecular weight range of 300-500 u) formed whereas lighter molecular tar decreased under the higher ER conditions. Tar removal performances of the gas cleaning system (the venturi scrubbers and the sawdust adsorbers) were also investigated. The tar removal efficiency of the gas cleaning system depended on gasification conditions, tar components and the amount of tar. Tar content in the syngas was reduced to 26-53% and 14-36% (by weight) at the exit of the scrubbers and sawdust adsorbers, respectively. By the action of this gas cleaning system, about 44% of light aromatic hydrocarbon tar was removed while no light PAH tar was detected at the exit of the gas cleaning system.     

Effect of urea management on yield and N use efficiency of lowland rice on an acid sulfate soil

Field experiments were conducted during 1988–1989 at two adjacent sites on an acid sulfate soil (Sulfic Tropaquept) in Thailand to determine the influence of urea fertilization practices on lowland rice yield and N use efficiency. Almost all the unhydrolyzed urea completely disappeared from the floodwater within 8 to 10 d following urea application. A maximum partial pressure of ammonia (pNH₃) value of 0.14 Pa and an elevation in floodwater pH to about 7.5 following urea application suggest that appreciable loss of NH₃ could occur from this soil if wind speeds were favorable. Grain yields and N uptake were significantly increased with applied N over the control and affected by urea fertilization practices (4.7–5.7 Mg ha^–1 in dry season and 3.0–4.1 Mg ha^–1 in wet season). In terms of both grain yield and N uptake, incorporation treatments of urea as well as urea broadcasting onto drained soil followed by flooding 2 d later were more effective than the treatments in which the same fertilizer was broadcast directly into the floodwater either shortly or 10 d after transplanting (DT). The¹⁵N balance studies conducted in the wet season showed that N losses could be reduced to 31% of applied N by broadcasting of urea onto drained soil and flooding 2 d later compared with 52% loss by broadcasting of urea into floodwater at 10 DT. Gaseous N loss via NH₃ volatilization was probably responsible for the poor efficiency of broadcast urea in this study.     

Application of a rice field experimental error distribution function to nitrogen-phosphorus-potassium fertilizer response model analysis

A distribution function of rice yield deviations from the mean was developed from field experiments with 555 plots at 16 sites in Zhejiang province, China, for three years. The deviation distribution in interval of 50kg/ha appeared as a symmetrical distribution with a high peak (Mean=0.279 [kg/ha], SD=240.686 [kg/ha]). Normality test using Kolmogrove-Smirnov test between the observed cumulative distribution and the normal cumulative distribution function indicates that the observed deviation distribution is not normal. An empirical exponential cumulative distribution function was developed. The distribution function was used to remove outliers during the development of a rice yield fertilizer response model, based on data from a non-replicated NPK field experiment.     

Attribution of sewage sludge and sludge-based char in a fluidized bed reactor

Fluidized bed pyrolysis has been recognized as an innovative technology for sewage sludge treatment. The physical and attrition properties of sewage sludge are changed through the fluidized bed pyrolysis. The minimum fluidization velocities and attribution rate constants for sewage sludge and sludge based-char were obtained from pressure drop and attribution tests. As a result, sewage sludge with 20% moisture content and char were classified as Geldart B solids and the superficial gas velocity for bubbling fluidization was 0.2142-0.8755 m/s. In addition, attribution of the sewage sludge and char was more affected by particle size than by material type. The equations for the overall attrition rate constants are K _a × 10⁵ = 1.09U − 14.82 for sludge and ln k _a = 0.1(U−U _mf )− 13.63 for char, respectively.