Dissolution of rock phosphate in silage leachate

Abstract

Following a favourable crop response to rock phosphate (RP) in a long term fertility trial in DeKalb, IL, an experiment was designed to dissolve RP in silage leachate on the premise that silage has a pH of 4.0 to 4.2 and that once drained of its leachate, it can be used for animal feed. Two types of RP, Brown Sugar RP and Ruhm's RP, having 30% P₂O₅ were dissolved in pure organic acids similar to those present in silage leachates. The amount of dissolved phosphorus (P) from RP in organic acids increased with organic acid:RP ratio. The highest amount of P dissolution was found with butyric acid. Thus, butyric acid with Brown Sugar RP, 2519, 1500, and 710 μg P/g RP were dissolved at 800, 400, and 200 acid:RP ratio, respectively; with Ruhm's RP the values were 3900, 1988, and 835, μg P/g RP, respectively. After dissolution of the two types of RP in the acids, there was an increase in solution pH of 1 to 2 units. Of the three types of silage leachates used, grass silage leachate had the highest acidity and calcium (Ca) concentration followed by high moisture and low moisture corn silage leachates, respectively. Soluble P concentration was five times higher in high moisture corn and grass leachates than in low moisture corn silage leachate. There was a decrease in acidity, Ca, and P content with the number of successive leachings. In low moisture corn silage leachate, 13.9 and 3.05 mg P/g Brown Sugar RP and 14.4 and 3.05 mg P/g Ruhm's RP were solubilized in the 1st and 2nd leaching, respectively. The study shows that corn low moisture silage leachate can dissolve RP efficiently and that it is a good, promising, and environmentally safe method for RP dissolution.     

中国洞庭湖区稻田土壤氮素淋溶损失的系统研究

A two-year lysimeter study was conducted to study the effects of different fertilizers and soils on nitrogen leaching loss in a double rice cropping system by considering three major types of paddy soils from the Dongting Lake area. The results showed that N concentration in the leachate did not differ significantly among the treatments of urea, controlled release N fertilizer and pig manure and that all these fertilizers produced higher total nitrogen (TN) concentrations in the leachate compared to the case where no fertilizer was applied. The TN leaching loss following urea treatment accounted for 2.28%, 0.66%, and 1.50% of the amount of N applied in the alluvial sandy loamy paddy soil (ASL), purple calcareous clayey paddy soil (PCC), and reddish-yellow loamy paddy soil (RYL), respectively. Higher TN loss was found to be correlated with the increased leachate volume in ASL compared with RYL, and the lowest TN loss was observed in the PCC, in which the lowest leachate volume and TN concentration were observed. Organic N and NH4+ -N were the major forms of N depleted through leachate, accounting for 56.8% and 39.7% of TN losses, respectively. Accordingly, soil-specific fertilization regimens are recommended; in particular, the maximum amount of fertilizer should be optimized for sandy soils with a high infiltration rate. To avoid a high N leaching loss from rice fields, organic N fertilizers such as urea or coated urea should primarily be used for surface topdressing or shallow-layer application and not for deep-layer application.     

UV-TiO2 Photocatalytic Degradation of Landfill Leachate

Mature landfill leachate contains some macromolecular organic substances that are resistant to biodegradation. The photocatalytic process helps to enhance biodegradability of landfill leachate. Batch experiments were employed to determine the optimum conditions for removal of organic matter by UV-TiO₂ photocatalysis. Under optimum conditions, the removal of chemical oxygen demand (COD), dissolved organic carbon (DOC), biological oxygen demand (BOD), and color was determined. Moreover, gas chromatography coupled with mass spectrometry (GC/MS) was used to analyze the organic matter in the treated leachate before and after treatment by the photocatalysis. The experimental results indicated that the removal of COD, DOC, and color by UV-TiO₂ photocatalysis could reach above 60%, 70% and 97%, respectively. Under optimal conditions, the ratio of biological oxygen demand (BOD)/chemical oxygen demand (COD) was elevated from 0.09 to 0.39, representing substantial improvement in biodegradability. GC/MS analysis revealed that 37 out of 72 kinds of organic pollutants in the leachate remained after 72 h treatment. Esters were produced during photocatalytic process and ketones, hydrocarbons, aromatic hydrocarbons, hydroxybenzenes, and acids were easier to be degraded during photocatalytic oxidation processes. The UV-TiO₂ photocatalysis systems proposed may be a cost-effective approach for pre-treatment of landfill leachate.     

Characterization of Compost Leachate Fractions Using NMR Spectroscopy

A distilled water leachate was prepared from a hardwood-leaf compost. The ¹³C NMR (nuclear magnetic resonance) spectra of organic acids isolates from this leachate provided support for the hypothesis that the composition of the dissolved organic carbon (DOC) in the leachate is very similar to that in natural soil pore waters. The leachate DOC was adsorbed by a model mineral surface, and the organic coating on the surface was characterized by solid-state ¹³C NMR spectroscopy.     

Accuracy of COD Test for Landfill Leachates

COD (chemical oxygen demand) has historically been considered to be an estimate of organic matter, and though this is no longer the case, for most kinds of water it is still a fair approximation. Landfill leachates may, however, be one of the exceptions. Landfill leachate contains many inorganic substances and, in certain circumstances, high concentrations of volatile organic compounds like acetic acid; the COD value may be affected by these conditions. Designed experiments were performed to determine how COD could be affected by the composition of landfill leachates. The factors studied include the content of iron(II), manganese(II), sulphide, ethanol, acetic acid, ammonia, and chloride as well as different aspects of the COD analysis design. The results show that up to about one-third of COD may be due to the inorganic components of leachates. The main conclusion from the experiments is that COD cannot be used solely as a measure of the organic matter of landfill leachate since inorganic substances as well as interactions between substances may interfere with the COD results.     

Efficiency of GAC for Treatment of Leachate from Soil Washing Process

Granular activated carbon (GAC), granular activated alumina (GAA) and a ferric chloride solution (FCS) were tested for the treatment of leachate contaminated by heavy metals. The leachate was collected following the remedation of soils using weak organic acids and/or their salts, EDTA and DTPA. Only GAC was found to effectively remove heavy metals (Cd, Cu, Cr, Hg, Mn, Pb and Zn as chelates) from the leachate. At optimum pH ranging from 5.4 to 6.9, 97% of Hg was removed while at optimum pH ranging from 6.9 to 7.7, 78 to 96% of Cd, Cu, Mn, Pb and Zn were removed. Some 77% of the Cr was removed at optimum pH of 5.4. Adsorption rate constant and Langmuir adsorption capacity of GAC were found to be 0.01 min^?1 and 19 mg metal chelate g^?1 of GAC, respectively. Freundlich constants, k and n were found to be 21 mg g^?1 and 2.778, respectively. The brown color of the leachate turned colorless after GAC treatment.

     

Effects of Leachate Irrigation on Landfill Vegetation and Subsequent Methane Emissions

Short-rotation tree forests are irrigated with landfill leachate to reduce both leachate volume and nutrient content. It is of interest both for leachate treatment and energy recovery to optimise the productivity of such plantations. This study's aim was to investigate the effects of irrigation on soil quality, tree growth and on emissions of landfill gas (LFG) produced in the wastes. Soils irrigated with leachate had a higher average nutrient and organic matter contents, and a lower dry solids content. Larger trees occur on plots irrigated with leachate, presumably due to the positive effect of water and nutrient supply. The willows used in this experiment seemed to be tolerant of high carbon dioxide concentrations, as no statistically effect arising from LFG emissions could be linked to tree growth. Methane oxidation levels between 50 and 950 mol m^-2 yr^-1 were observed. The positive correlation between soil methane oxidation capacity and tree presence is an interesting perspective on reduction of methane emissions by landfill's top cover vegetation type. Optimising methane oxidation using vegetation as a ‘cover crop’ could reduce the amount of methane discharged into the atmosphere.     

Toxic effect of landfill leachate on microalgae

Leachates from two landfills, namely Junk Bay (JB) and Gin Drinkers' Bay (GDB), were assessed for their acute toxicity using four green algal species, Chlorella pyrenoidosa, C. vulgaris, Scenedesmus sp. and Dunaliella tertiolecta. JB leachate was more toxic to the four algal species tested than leachate from GDB landfill. The growth rates of all four species in 50% JB leachate, and two species (C. vulgaris and D. tertiolecta) in 50% GDB leachate were significantly lower (P<0.05) than those in the control (Bristol Medium only). Values of 96h-EC50 of JB leachate for all four species were lower than those of GDB. The high contents of ammoniacal-nitrogen and organic compounds (such as volatile fatty acids) seemed to be the factors governing the toxicity of leachate on algae. There were differential sensitivities to leachate exhibited by the tested algal species. Susceptibility to leachates in terms of cell number were in the ascending order of C. pyrenoidosa, Scenedesmus sp., C. vulgaris and D. tertiolecta.     

渗育性水稻土渗滤液中的磷组分研究

本试验在太湖地区长江岸边砂质渗育性(漏水型)水稻土上进行,研究在麦稻轮作条件下连续两年施用不同磷肥(每季P 0、30、70、150和300 kg hm-2),稻季各层次土壤溶液中(30、60和90 cm)磷的组分,以探讨磷素在剖面中垂直纵向移动的规律。结果表明:施肥处理在施肥初期提高了30 cm处土壤溶液中溶解磷浓度,对60 cm处溶解磷浓度影响不大,对90 cm处溶解磷浓度没有影响。各处理60 cm和90 cm处土壤溶液中溶解磷的浓度几乎全部超过水体富营养化磷的阈值,故在研究该地区水体富营养化时,要注意渗漏磷排放可能的贡献。特别应指出的是,除6月13日对照处理外,各处理90 cm处土壤溶液中的磷均以溶解有机磷为主,占总溶解磷的56%~100%,表明有机磷(外源加入或内源残留的)比无机磷对环境的潜在威胁将更大。     

Topographical Influences on the Spatial Distribution of Soil Mercury at the Catchment Scale

The catalytic effect of Cu(II) on the formation of disinfection by-products (DBPs) and chlorine degradation during chlorination of humic acid (HA) solutions was comparatively investigated under different experimental conditions. The experimental results showed that the total organic halogen (TOX) and trihalomethane (THM) formation increased with increasing Cu(II) concentration during chlorination, while haloacetic acids (HAAs) increased insignificantly. Accelerated chlorine decay and increased TOX and HAA formation were observed at high pH in the presence of 1.0 mg/L Cu(II) compared with that observed at low pH but THM formation decrease. Furthermore, the Cu(II) effect catalyzed the formation of brominated DBPs as it did for chlorine analogues in the presence of bromide ion. The microcalorimetry analysis demonstrated that more DBPs were formed in the Cu(II)-catalyzed chlorination, in which second-order rate constants obtained from reaction of HA with chlorine under given experimental conditions were 0.00256 M^?1?s^?1 (without Cu(II)) and 0.00865 M^?1?s^?1 (with Cu(II)), respectively. To discriminately examine the role of Cu(II) in greater detail, nine model compounds, which approximately represent the chemical structural units of HA, were individually oxidized by chlorine. It was demonstrated that carboxylic acids significantly enhanced the formation of TOX, THMs, and HAAs in the presence of Cu(II). Based on the previously published information and our experimental results, the possible pathway for Cu(II)-catalyzed TOX, THM, and HAA formation from chlorination of carboxylic acids were tentatively proposed.     

Water-soluble organic materials in paddy soil ecosystem

Abstract

A column experiment was conducted to analyse the composition of organic materials in the leachate from the plow layer and their fate in the subsoil. Water-soluble organic materials in the leachate were fractionated by insoluble polyvinylpyrrolidone (PVP) and ion exchange resins. The content of total organic carbon (TOC) in the leachate increased by the addition of rice straw (RS) to the plow layer soil sample. The leachate contained a constant amount of PVP-adsorbed Fraction, while that of the PVP-non-adsorbed Fraction changed during the 45 day incubation period. In the fractionation using ion exchange resins, the fraction adsorbed onto the anion exchange resin was the major one.

By the connection of a subsoil column to the plow layer soil column with RS, the TOC content in the leachate decreased by percolation into the subsoil sample. In the Anjo soil sample (Yellow Soil), the decrease occurred throughout the incubation period, and about 90% of the PVP-adsorbed Fraction in the leachate decreased by percolation into the subsoil sample. In the Fukushima soil sample (Gray Lowland Soil), the TOC content decreased in the early and middle periods of incubation, while in the late period the decrease was negligible. This decrease of the TOC content by percolation into the subsoil sample was mainly due to retention in the subsoil sample of the Anjo soil, while in the Fukushima soil sample it was due to decomposition and retention. It was considered that easily decomposable organic materials like organic acids were decomposed in the early to middle periods of incubation, while in the late period the contents of such substances in the leachate from the plow layer soil sample with RS were small and the decrease of TOC was negligible.     

Comparative assessment of the chemical and adsorptive characteristics of leachates from a municipal and an industrial landfill

Leachates from two landfills, one municipal and one industrial, were compared with respect to their chemical and adsorptive characteristics. Concentrations of most inorganic constituents were as much as an order of magnitude higher for the industrial leachate. The concentration of organic matter in that leachate, measured as total organic carbon (TOC), was more than two orders of magnitude greater than that of the municipal leachate. Gel permeation studies suggested similar molecular weight distributions for the organic fractions of the two leachates, but specific priority pollutants identified were different. The adsorptive characteristics of the waste samples with respect to activated carbon were evaluated using TOC as a lumped parameter expression of organic matter concentration. Adsorption equilibria and rates for the municipal leachate system were reasonably well described by treating TOC as a single component for modeling purposes. The industrial ieachate required a multicomponent approach. Ideal adsorbed solution theory was used in this case to characterize the behavior of a set of hypothetical TOC components. The approach was able to account, to some degree, for the competitive interactions evident among organic solutes comprising the mixture.     

Halogenated phenols in water at forty Canadian potable water treatment facilities

Samples of raw and treated water were collected once in each of 3 seasons at 40 potable water treatment plants across Canada and were analyzed for phenol and 33 halogenated phenolic compounds including chlorophenols, bromophenols, bromochlorophenols, and chloroguaiacols. Eighteen of the compounds were not found at any treatment plant; phenol and each of the remaining halogenated phenols were found in at least 1 sample. Pentachlorophenol was the only halogenated phenolic compound found in more than 20% of the raw water samples in the fall and winter samples at levels up to 53 ng/L with mean values of 1.9 and 2.8 ng/L, respectively. No halogenated phenols were detected in raw water summer samples. The halogenated phenols found most frequently in treated water samples were 4-chloro-, 2,4-dichloro-, 2,4,6-trichloro-, and bromodichlorophenols. Mean values were less than 15 ng/L and maximum values seldom exceeded 100 ng/L. Most of the positive values for the treated water samples were found at 8 of the 40 treatment plants but no correlations could be found between halogenated phenol levels and raw water type, treatment process, or chemical dosages.     

Water-soluble organic materials in paddy soil ecosystem

Abstract

Column experiments were conducted to analyze the effect of the temperature on the amounts of organic materials in the leachate, especially organic acids and methane, from samples of the plow layer soil amended with rice straw. Total amount of inorganic carbon in the leachate during the 30-d period of incubation in relation to the temperature was 18°C < 25°C ≤ 30°C > 37°C > 45°C. Total amount of organic carbon in the leachate was signiicantly larger under 45°C incubation than that at other temperatures.

Acetic acid was the dominant organic acid in the leachate regardless of the temperature. Butylic and propionic acids were also present in large amounts in the early and the late period of incubation of temperatures ranging between 18 and 37°C, while only acetic acid was the dominant organic acid during the 30-d period of incubation at 45°C.

The total amount of methane in leachate during the 30-d period of incubation was very small at 18°C, while very large at 25, 30, and 37°C. It decreased nearly to one half at 45°C compared with that at 30°C. Based on the values of δ¹³CH₄ in the leachate, 3 different stages were recognized in the predominant processes of methane production in the submerged paddy soil amended with rice straw: the stage when methane production from CO₂-B₂ was predominant followed by the stages of methane production from acetic acid and from CO₂-H₂ in this order. The second stage coincided with the time of decrease of the organic acid contents in the leachate. Under 45°C incubation, methane production from CO₂-H₂ was predominant throughout the 30-d period of incubation.     

有机无机肥配施对玉米产量及土壤氮磷淋溶的影响

【目的】氮、磷是农作物生长所必需的营养元素,对提高农作物产量和改善产品品质均有重要作用,但由于肥料不合理施用,农田土壤中养分大量盈余,在降雨或灌溉条件下易随水流失,导致水环境质量下降。因此,研究有机无机肥料配施对土壤氮、磷淋溶风险的影响,可为地下水环境质量保护提供依据。【方法】采用田间渗滤池法,对华北地区玉米季氮磷淋溶状况连续5年进行监测,具体施肥处理如下:对照(不施用氮肥,PK)、单施化肥(NPK)、单施有机肥(与NPK处理等氮量,SW)、有机肥无机肥料配施(用猪粪中氮替代50%NPK处理中氮用量,SNP)。采集120 cm处淋溶水,测定氮、磷含量,研究在总氮投入量相同条件下,有机无机肥料配施对华北地区玉米产量及土壤剖面120 cm处氮磷淋溶的影响。【结果】1)有机无机肥料配施(SNP)处理,可以保证玉米较高产量,5年平均产量较单施化肥处理(NPK)提高10.3%。2)有机无机肥料配施可以显著减少总氮(TN)淋溶量,SNP处理较NPK处理减少71.4%;NPK处理淋溶水中NO-3-N浓度显著高于SNP处理,其平均浓度分别为54.93 mg/L、13.47 mg/L。3)在等氮量投入条件下,有机肥的投入带入了大量磷素,单施有机肥(SW)较NPK处理总磷(TP)淋溶量增加了0.6倍,分别为0.056 kg/hm2、0.035 kg/hm2;淋溶水中TP浓度分别为0.09 mg/L、0.066 mg/L。在氮磷养分淋溶损失中,NO-3-N占淋溶水TN的80%以上,可溶性总磷(TDP)占淋溶水TP的70%左右。4)在监测淋溶水中,NPK处理NO-3-N平均浓度已超过我国地下水Ⅲ类水质量标准(GB/T 14848-9),SW处理TP平均浓度0.09 mg/L,也高于水体富营养化TP浓度(0.02 mg/L)的临界值,可对水体造成污染。【结论】在氮磷养分淋溶损失中,NO-3-N占淋溶水TN的80%以上,TDP占淋溶水TP的70%左右。采用猪粪氮替代50%化肥氮素的有机无机肥料配施处理,5年玉米平均产量显著高于单施化肥处理,证明该施肥方法不仅可以确保产量,还可降低氮素淋溶,基本保证淋溶水中NO-3-N浓度低于地下水Ⅲ类水质量标准(GB/T 14848-9)。     

Polybrominated Diphenyl Ether Leachability from Biosolids and Their Partitioning Characteristics in the Leachate

Biosolids are commonly applied to agricultural soils. A laboratory investigation was carried out to determine polybrominated diphenyl ether (PBDE) congener profiles in biosolids and leachability by water. In addition, PBDE fractionation in water and suspended solids of different sizes was examined to determine the potential for enhanced mobility of these contaminants within soils. The leachates from glass column experiments were passed through a series of filters, and the filtrates and retained particles analyzed for PBDEs. PBDEs were found to sorb on solid particles suspended in the leachate, allowing PBDEs to be present at concentrations exceeding their aqueous solubilities. The filtration process indicated that PBDEs are associated with fine and ultrafine particles. Filters of different pore sizes provide a better indication of PBDE levels in the leachate compared to not filtering or using a single filter. PBDEs concentrations were much higher on ultrafine than on fine particles, due to the greater surface area and higher organic content of the former.     

Effects of soil drying and rate of re-wetting on concentrations and forms of phosphorus in leachate

The drying and re-wetting of soils can result in the modification of the amounts and forms of nutrients which can transfer, via leachate, from the soil to surface waters. We tested, under laboratory conditions, the hypothesis that the rate of re-wetting of a dried soil affects the solubilisation and concentrations of different forms of phosphorus (P) in leachate. A portion of grassland pelostagnogley soil (sieved moist <2 mm) was dried at 35°C and another portion maintained at approximately 40% water-holding capacity. Water (25 ml) was added at ten regularly spaced time intervals in 2.5-ml aliquots to the surfaces of both soils over periods of 0, 2, 4, 24 and 48 h, resulting in different rates of application. The leachate was collected and analysed for dissolved (<0.45 μm) and particulate total P and molybdate reactive and unreactive P. The rate of re-wetting significantly changed the concentrations of P, especially dissolved forms, in the leachate. Dissolved P concentrations were highest in leachate from the 2-h treatment, while particulate P concentrations were highest in the 0-h treatment leachate. In all cases, most P was unreactive and, therefore, likely to be in an organic form. Soil drying decreased microbial biomass, but this could not be directly linked to an increase of P in leachate. These results suggest that changes in patterns of rainfall frequency and intensity predicted by climate change scenarios could significantly affect the quantities of P leached from soils.     

Organic priority pollutants in groundwater and surface water at three landfills in north central Florida

The occurence of organic priority pollutants in groundwater and surface water impacted by municipal landfill leachate was studied at the Orange County Landfill in Orange County, Florida. The results of the investigation were compared to existing data from two municipal landfills in Alachua County, Florida. The investigation in Orange County evaluated existing wells and surface water stations through sampling of groundwater, surface water, sediment, and aquatic biota. Very few organic priority pollutants were detected. The constituents most frequently found were volatile organic compounds, particularly aromatic organic constituents. Volatile organic compounds were detected in groundwater at total concentrations of less than 100 Μg L^?1. Few base/neutral and acid extractable organic priority pollutants were detected. Data from the Alachua County landfills indicated the presence of volatile organic compounds in groundwater at both landfill sites but few organic priority pollutants in the base/neutral and acid extractable group were fouund. Any organic priority pollutants that were present in the solid waste as deposited were likely metabolized by microorganisms or otherwise degraded, sorbed on particulate matter, or diluted to such an extent as to be non-detected.     

Studies on The Mechanism of Root Damage of Rice Plants in The Peat Paddy Field (Part 2)

In the previous paper (1), it was assumed chat some inhibitory soil substances in submergel peaty soil, such as ferrous iron, sulfide, organic acids, and unknown minor organic substances like humus subordinaten might have contributed to root damage. This assumption is draven from the results of the soil leachate experiments. Two other subjects to be investigated for full understanding of the mechanistu of root damageare are:     

人工湿地系统在垃圾渗滤液处理中的应用

人工湿地是一种很有前途的废水处理方法,具有对污染物的去除能力强、基建和运行费用低、维护管理方便、耐冲击负荷能力强等优点。对人工湿地系统在垃圾渗滤液处理中的表现进行了分析,结果表明,其对有机物、氮磷和金属元素均具有较高的去除率,利用人工湿地处理垃圾渗滤液的方法具有广阔的应用前景。