Evaluation of organic matter stabilization in sewage sludge

Abstract

The ratio between non‐humified and humified fractions in pyrophosphate extracts is shown to vary during maturation of sewage sludge. The ratio is higher than 1 in the raw materials but lowers at 1 or less than 1 with the aging of sludge and is assumed to reflect quantitatively the degree of stabilization of organic matter in the sludge. Analytical isoelectrofocusing (IEF) experiments showed that humified fractions in raw sludge focalize only in the pH gradient regions lower than 5.0, whilst in older sludge samples a progressive strengthening of bands occurs in the region between pH 6.5 and 5.0, approaching at least partially IEF patterns of soil organic matter. IEF patterns are suggested to reflect the stabilization of organic matter in sewage sludge from a qualitative point of view.     

污泥土地利用研究：Ⅲ、富锌污泥

西通过温室盆栽试验方法研究不同富锌污泥施用方法对水稻生长及其重金属含量的影响，结果表明，污泥施用主要通过增加水稻分蘖来促进水稻生长从而提高产量。污泥的施用显提高了水稻茎叶和籽粒中锌的含量。     

污泥土地利用研究：—Ⅴ．高铜污泥

本采用田间小区试验方法研究了高铜污泥对辣椒生长、Vc含量和重金属含量的影响。结果表明，污泥施用量在3．75和7．5t/hm^时，辣椒各个生长指标都有所增加，有些指标都有所增加，有些指标甚至优于施用化肥处理。污泥施用对辣椒果实Vc含量没有明显降低的趋势，污泥施用未显地增加辣椒植株和果实对铜、锌、镉和镍的吸收。     

污泥土地利用研究：Ⅳ、无锡污泥与香港碱化污泥的肥效比较

本通过盆栽试验研究了污泥施用对青菜和番茄生长的影响，试验表明，污泥施用可显促进青菜和番茄的生长，但和长在酸酸性红壤和太源水稻土上两种蔬菜对污泥施用的响应不同，香港碱性污泥产品对青菜在酸性红壤上的增产效果优于无锡污染；无锡污泥随施用量增加产量有所增加：太湖水稻土上无锡污泥的肥效优于香港碱性污泥产品。污泥施用不仅对当茬蔬菜增产明显，对后茬蔬菜也有增产效应。     

Labile water soluble components govern the short-term microbial decay of hydrochar from sewage sludge

Due to higher proportions of labile carbon (C) compounds the suitability of biochar produced by hydrothermal carbonization (HTC) for C sequestration is questionable. We hypothesized that pre-treatment with water would reduce the biological decay of hydrochar from sewage sludge. Unwashed and washed feedstock and hydrochar were incubated in a short-term experiment. The kinetics of the biological decomposition of the materials was calculated on the basis of a double exponential model and the C sequestration potential using the CANDY Carbon Balance (CCB) model. Biological decomposition of the carbonized materials was governed by the percentage of labile C compounds. Mean residence time of a fast (MRT_fast) and slow decay pool (MRT_slow) of unwashed hydrochars varied clearly (MRT_fast: 0.8 – 5.0 months and the MRT_slow: 5.0–18.6 months). The pre-treatment with water removed labile hydrochar C and reduced the biological accessibility. MRT_fast and MRT_slow was increased by intensive washings (MRT_fast: 5.0–7.4 months and the MRT_slow: 14.9 months). High synthesis coefficients suggest that hydrochar C was humified and transferred into stabilized SOC. The results clearly show that once adsorbed components were eliminated, and as compared to pyrolysed biochar hydrochar from sewage sludge may also be useful for soil C sequestration.     

Effects of sewage sludge disposal

The disposal of sewage sludge affects the environment as the sludge May, contain harmful components such as pathogenic organisms, organic compounds, heavy metals and excess phosphorus and nitrogen. Depending on the method of disposal, these effects can be immediate or time-delayed and non-linear. the effects of dumped or landfilled sewage sludge can be characterized through its leaching capability, which depends on the treatment before dumping. Treatment May, be simple dewatering or advanced incineration, wet oxidation or immobilization. Leach-ability is considered here.     

污泥土地利用研究：Ⅱ、连续化学提取法研究施污泥土壤重金属的有效性和环境风险

本文采用连续化学提取法研究了施用污泥土壤中重金属的形态分配及有效性。铜和在2种土壤上施用污泥前、后的形态分配都有所差异，铜在 湖相水稻土上可以氧化态为主：红壤性水稻土可氧化态和可还原态含量都较高。锌在河湖相水稻土以可还原态为主，在红壤性水稻土以醋酸溶解态为主，两种土壤上，铜和锌的3种不同形态含量与污泥施用量之间都有很好的相关性，连续提取对于研究重金属的形态分配比单独提取更有价值。     

Medically used radionuclides in sewage sludge

The concentration of medically used radionuclides has been studied in sludge from the sewage treatment plant serving the borough of Malmo. In this area all nuclear medicine procedures are carried out in one hospital and almost all patients live in the borough. Therefore, the input of medically used radionuclides into the sewage system can be estimated with good accuracy. Samples of digested sludge have been taken once or twice a week during half a year. Iodine-131 (physical half life (T) = R.05 d) was detected in all samples. The ¹³¹I-activity concentration due to medical use varied between (0.03±0.01) and (0.12±0.02) nCi kg^?1. The ratio between the total output of ¹³¹I via the sludge and an adherent input of the radionuclide into the sewage system was determined to (2.6 ± 0.6) × 10^?3, which is equivalent to a ratio of (2 ± 1) × 10^?2 for stable I. Occasionally measurable activities of ¹⁹⁸Au (T=2.7 d) and ²⁰¹T1(T=3.l d) have been found. The radioactivity concentration of medically used radionuclides in the sludge is low and constitutes no health problems for the persons involved. The sludge however has proved to be a very sensitive and suitable integrator of radioactive material released from a large urban area.     

Copper species in aqueous sewage sludge extract

The Cu in the saturation extract of dried Davis sewage sludge was mainly in a complexed form. A Cu²⁺ specific ion electrode was used to determine the extent of complexation. The adsorption coefficient for the complexed Cu on Yolo silt loam was 4 while for Cu added as CUSO₄ it was 90 L kg^?1 at relevant Cu concentrations in solution. Paper electrophoresis was used to define the Cu complexes according to their mobility in an electric field. Six fractions of positive, negative and neutral charge were isolated. The portion of Cu in the sludge which was water soluble increased significantly upon drying. The large percentage of complexed Cu and its relatively low adsorption on soil suggested that sewage sludge may, under certain conditions, be a source of Cu contamination of plant systems and, in extreme cases, of ground water.     

The fate of metals in sewage sludge incinerators

The fate of heavy metals in multiple hearth sewage sludge incinerators was examined using mass balance techniques. All major process streams into and out of the incinerators were sampled in order to characterize the partitioning of Cu, Ni, Ph, and Cd into the major effluent streams, and to calculate a metals mass balance around the incinerators. The results indicate that the residual particulate matter from the incineration process becomes progressively more enriched in the more-volatile metals (Cd and Ph) with decreasing particulate size, in the order bottom ash < cyclone ash < scrubber water particulate < stack particulate. The less-volatile metals Cu and Ni are not similarly enriched. The mass balance indicates that approximately two-thirds of the Cd mass entering the incinerators is partitioned to the scrubber water stream, while the bottom ash stream receives most of the Cu, Ni, and Pb.     

Molybdenum hazard in land disposal of sewage sludge

The application of sewage sludge to agricultural fields may result in the production of Mo-rich herbage, a cause of metabolic disorders in animals. An alternative to application of sludge to agricultural fields is sludge utilization in strip-mine reclamation. Oxidation of strip-mine spoil material causes accumulation of Mo-rich iron oxyhydroxide in stream beds and spoil piles. Strip-mine reclamation by sludge application may induce short-term increases in the concentration of Mo and other metals in waters discharged from the reclaimed area because of pH dependent ion-exchange reactions and dissolution of Mo-bearing iron oxyhydroxides.     

Effect of sewage sludge on nitrogen availability in peat

Summary We studied the effect of incubating peat with lime and sewage sludge in small proportions on biological activity and N mineralization. The peat response was dependent on pH and, in acid peats, on mineralization capacity. In acid peats, the addition of sewage sludge inhibited biological activity. Only the most eutrophic peats (Herbosa) responded with accelerated mineralization. The addition of lime to acid peats favoured organic matter mineralization, shown by a greater CO₂ release. The best results were obtained by adding lime and sewage sludge together. In saline peats, the best N levels were obtained without incubation.     

Monitoring biochemical activity during sewage sludge composting

A sewage sludge with the addition of two woody materials (1 : 2 ratio), tree-pruning chips and vine shoots, to provide structure were composted under controlled conditions of temperature (28°C) and humidity (70% ambient humidity). Hydrolytic enzyme activities [urease, phosphatase, N-benzoil l-argininamide (BBA) hydrolysing protease, casein-hydrolysing protease, ATP, hydrosoluble and hydrolysable polysaccharides] were determined during the aerobic incubation. Samples were taken and incubated under the same conditions in an accelerative bioreactor to test potential C mineralisation by measuring the CO₂ evolved. A rapid mineralisation phase (2–3 weeks) was followed by a slow maturation (4–14 weeks) period. The slow phase and the dynamics of substrate decomposition were better indicated by the hydrolytic enzyme activities that were measured. The structuring agents slightly retarded the compositing process with tree prunings having the strongest effect. Hydrolysable polysaccharides and Folin-reactive compounds (proteins, polyphenols) released by the structure-providing lignocellulose material appear to have controlled both the intensity and the length of the maturation phase.     

Effects of sewage sludge amendment on soil aggregation

Sewage sludge in doses of 200 and 400 Mg ha⁻¹ (dry weight) were applied in an experimental rehabilitation of a limestone quarry to improve soil physical condition. The effect of this organic waste on soil aggregation and structural stability has been tested measuring aggregate size distribution by dry- and wet-sieving procedures over a period of 28 months. We discuss the influence of the organic components of aggregates on soil structure. The main effect of sewage sludge was to increase aggregate stability to raindrop impact (splash) just after application of the former but one year later this effect decreased notably. Organic matter is distributed in different ways between macro- and microaggregates, and this parameter seems to be responsible for the structure changes observed. Copyright © 1999 John Wiley & Sons, Ltd.     

Heavy metals in mine soils amended with sewage sludge

In order to reclaim a clay quarry, a topsoil material was mixed with gravelly spoil at different ratios and with various rates of sewage sludge. The influence of three spoil/topsoil ratios (1:1, 2:1 and 3:1) and three sludge rates (40, 80 and 120 t ha⁻¹) on chemical properties of the resulting material was investigated, with emphasis on heavy metal (Fe, Cu, Mn, Ni and Zn) contents. The mixtures topsoil/spoil/sludge were water saturated and incubated for 15 or 30 days in a chamber under controlled conditions. The incubated samples were analysed for pH, total carbon and nitrogen, and total, available, exchangeable and soluble heavy metals. The addition of spoil to the topsoil increased the volume of material available, by utilizing an inert material unsuitable by itself to grow plants. The addition of sewage sludge repaired the disadvantages of the spoil, increasing the pH and the organic matter contents. The total heavy metal contents in the mixtures followed the sequence Fe>>Mn>>Zn, Cu>Ni. All except Cu were within the ranges allowed for agricultural lands. The available heavy metals constituted a small fraction of total contents and decrease with time due to complexation and immobilization processes. The exchangeable and soluble fractions were almost negligible; only small amounts of Mn, Zn and Cu were detected. Therefore, the risk of contamination by heavy metals is insignificant in the conditions investigated. Copyright © 1999 John Wiley & Sons, Ltd.     

Mutagenic potential of municipal sewage sludge amended soils

This study was conducted to measure the mutagenic potential of municipal sewage sludge amended soil. Two separate sludge samples were collected from one municipal wastewater treatment plant and applied to undisturbed soil lysimeters over a 9 mo interval. Soil and sludge samples were collected for approximately 2 yr following sludge application. Samples were solvent extracted using methylene chloride and methanol, and the bacterial mutagenicity of the resulting residue determined using the Salmonella/microsome assay. The maximum specific activity of the sludge amended soil was 416 net revertants per 10 mg of residue induced by the methanol fraction extracted from the Weswood soil collected 154 d following the first sludge application. In the Padina sand, the maximum specific activity was 320 net revertants per 10 mg of residue induced by the methanol fraction extracted from the sample collected 154 d following the first sludge application. The specific activity of the sludge amended soil was observed to decrease slowly with time. For both the Padina and the Weswood soils, mutagenic organic chemicals were detected in soil samples collected 510 d following the second sludge application. For the Weswood soil, the mutagenic activity per unit weight of soil with metabolic activation of the samples collected 510 d after the final sludge application was decreased by 15 and 76% for the methylene chloride and methanol fractions, respectively, when compared to the maximum weighted activity observed 56 d after the final sludge application. The results indicate that municipal sewage sludges may contain organic mutagens which are persistent in the soil.     

Trace metal analysis of sewage sludge and soils in Bahrain

Trace metals such as Pb, Zn, Cu, Ni, Cd and Fe were determined in sewage sludge produced at a sewage treatment plant in Bahrain (Tubli) and soils. The soils, both untreated and treated with the sludge, are used for agricultural purposes in Bahrain. The Trace-metals level showed the following range (μg g^?1 dry weight); Pb, 242 to 609; Zn, 704 to 836, Cu, 329 to 512; Ni, 23 to 41; Cd, 1.8 to 3.9 and Fe, 1867 to 4284. The data show the degree to which untreated soils have already been contaminated with trace elements. The level of trace-elements found in sludge showed the following range (μg g^?1 dry weight); Pb, 140 to 186; Zn, 597 to 836; Cu, 348 to 449; Ni, 47 to 53; Cd 5.7 to 9.2 and Fe, 5950 to 8520. Mean levels were generally close or lower than mean concentration reported in the United Kingdom and the United States for sludge. They were also lower than the suggested concentration limits for application of sludge on agricultural land, which is one of the most cost effective and attractive techniques for sludge disposal. Soils treated with this sludge (after 1 yr) were also analyzed and showed substantial enhancement of the available level of trace elements in the soil. This eventually will lead to an increase in the trace-element level in plants grown for human or animal consumption. This could have phytotoxic effects, and the possibility of toxic effects on live-stocks and human beings.     

The speciation of metals in sewage and activated sludge effluent

A gel filtration chromatography technique was used to separate soluble species of Cd, Cu, Co, Mn, Ni, and TI in the influent and effluent of a laboratory scale activated sludge simulation operated at a range of sludge ages from 3 to 18 days. It was found that, whilst there was no general trend for all six metals, Cd and Mn associated mainly with low molecular weight fractions; Co, Cu, and Ni with a range of predominantly high molecular weight fractions; and TI tended towards association with high molecular weight fractions which influenced metal solubility and appeared to be significant in determining metal removal. It appeared that all metals exhibited high affinity for mixed liquor suspended solids (MLSS) and that this affinity was strongest for Cu and Cd. Nickel, Co, Cu, and TI appeared to show a high affinity for polymeric microbial products produced at longer sludge ages. The gel filtration technique was found to be useful in the separation of metal species in conjunction with a sufficiently sensitive detector provided their concentrations in the original sample were relatively high.