Alum Sludge Dewatering Using Moringa oleifera as a Conditioner

An active component of Moringa oleifera (MO) has been used in comparison with synthetic polymers and alum for the conditioning of chemical sludge from a drinking water treatment plant. The comparison was based on dewatering characteristics of the conditioned sludge determined by capillary suction time (CST), specific resistance to filtration (SRF), sand column drainage and shear strength tests. The results indicated that MO showed comparable conditioning effect as alum. Polyelectrolytes were more effective than MO and alum. Sludge conditioned with MO and alum, as in dual chemical conditioning, showed better results than MO alone. According to CST, SRF and sand drainage results, optimum doses for MO, alum and polyelectrolytes were 125, 63, and 1.8 kg/t, respectively. Comparison of the two polyelectrolytes showed that the cationic polyelectrolyte was more effective. For sand drainage tests both polyelectrolytes improved the drainage rate by 2 orders of magnitude. MO and alum improved the drainage rate by about 4.2 times. On the other hand, the improvements in cake solids concentration were similar for all the chemical conditioners. Flocs from MO and alum were relatively stronger compared to those of the polyelectrolytes. From the results of the study it could be concluded that MO alone or in combination could be effectively used and replace alum for dewatering of chemical sludge.     

Environmental evaluation of sewage sludge application to reclaim limestone quarries wastes as soil amendments

Restoration of degraded soils with organic wastes could be a feasible practice to minimize erosion in the Mediterranean area, but with the risk of soil and groundwater pollution. Currently the use of sewage sludge to improve the nutrient contents of a soil is a common practice. The soil to which a great amount of fertilizers is usually applied, may favour the solubilization of inorganic compounds. In order to study the mobility of some of these elements through the soil, we designed an experiment aimed to reproduce the behaviour of different compounds and heavy metals in the soil as a part of the non-saturated zone. A controlled experiment in a greenhouse using soil columns was used. A mineral residue from a limestone quarry in Alicante (south-east of Spain) was amended with 30 and 90 t of sludge ha⁻¹. Nitrate, ammonium, cadmium, and nickel were analysed in leachates collected at the bottom of the columns. We found high concentrations of nitrates and ammonium in leachates, which imply an important environmental risk. No important displacements of Cd and Ni were found.     

Long-term exposure to Zn-spiked sewage sludge alters soil community structure

An 8 year study to investigate the effects of Zn-spiked sewage sludge additions on the microbial community structure and microbial processes was carried out in a field soil under pasture. The microbial community structure was evaluated using a combination of multiplex-terminal restriction fragment length polymorphism (M-TRFLP) and T-RFLP fingerprinting approaches. Soil respiration, microbial biomass and enzymatic activities were measured as indicators of soil microbial processes. Changes in the microbial community structure, with Zn additions were evident in all the microbial groups investigated (bacteria, fungi, archaea, actinobacteria and rhizobia/agrobacteria). The fungal community showed the greatest response to Zn additions compared to the other microbial communities measured. The relative abundance of several fungal terminal restriction fragments (TRFs) significantly increased in high Zn treated treatments, at the expense of others, some of which were lost from T-RFLP profiles completely. These results indicate that metal-spiked sludge application can have long-lasting impacts on the composition of the microbial community in pasture soils. Despite notable changes in community structure there was no significant long-term impact of Zn-spiked sludge applications on microbial respiration, biomass or enzyme activities.     

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.     

生物强化技术在污泥堆肥处理中的效果

为了探究生物强化技术在污泥堆肥处理中的优势,以接种量分别为0.2%和0.4%的复合生物菌剂研究对污泥堆肥的作用效果,分析了温度、有机质含量、铵态氮、硝态氮、重金属含量、蛔虫卵死亡率和种子发芽指数(GI)的动态变化,结果表明:接种复合生物菌剂处理较对照组(CK)对堆肥指标有一定的影响,能够提高堆体升温速率及延长高温持续时间、加速有机质的降解、促进铵态氮与硝态氮的转化、降低重金属含量、提高蛔虫卵死亡率、提高种子发芽指数,其中复合生物菌剂接种量为0.4%时作用效果较为明显,有利于污泥堆肥。     

Growth and nitrate reductase activity in Juniperus oxycedrus subjected to organic amendments and inoculation with arbuscular mycorrhizae

The effectiveness of reforestation programs on degraded soils in the Mediterranean region is frequently limited by a low soil availability and a poor plant uptake and assimilation of nutrients. While organic amendments can improve the nutrient supply, inoculation with mycorrhizal fungi can enhance plant nutrient uptake. A pot experiment was conducted in 2004 to study the influence of inoculation with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola Trappe, Bloss. & Menge, and G. mosseae (Nicol & Gerd.) Gerd. & Trappe) and of an addition of composted sewage sludge or Aspergillus niger–treated dry‐olive‐cake residue on plant growth, nutrient uptake, mycorrhizal colonization, and nitrate reductase (NR) activity in shoot and roots of Juniperus oxycedrus L. Six months after planting, the inoculation of the seedlings with G. intraradices or a mixture of three AM fungi was the most effective treatment for stimulating growth of J. oxycedrus. There were no differences between the two mycorrhizal treatments. All treatments increased plant growth and foliar N and P contents compared to the control plants. Mycorrhizal inoculation and organic amendments, particularly fermented dry olive cake, increased significantly the NR activity in roots.     

施用碱稳定固体的酸性土壤的Cu和Zn的形态分布

Fractionation of metals in a granite-derived acid sandy loam soil amended with alkaline-stabilised sewagesIudge biosolids was conducted in order to assess metal bioavailability and environmental mobility soil solution was extracted by a centrifugation and filtration technique. Metal speciation in the soil solution wasdetermined by a cation exchange resin method. Acetic acid and EDTA extracting solutions were used forextraction of metals in soil solid surfaces. Metal distribution in different fractions of soil solid phase was determined using a three-step sequential extraction scheme. The results show that the metals in the soilsolution existed in different fractions with variable lability and metals in the soil solid phase were also presentin various chemical forms with potentially different bioavail ability and environmental mobility Alkaline-stabilised biosolids could elevate solubility of Cu and proportion of Cu in organically complexed fractionsboth in soil liquid and solid phases, and may therefore increase Cu mobility. In contrast, the biosolids lowered the concentrations of water-soluble Zn (labile fraction) and exchangeable Zn and may hence decrease bioavailability and mobility of Zn. However, Fe and Mn oxides bound and organic matter bound fractions are likely to be Zn pools in the sludge-amended soil. These consequences possibly result from the liming effect and metal speciation of the sludge product and the difference in the chemistry between the metals in soil.     

Modelling nitrate and bromide leaching from sewage sludge

A deterministic model for assessing the risk of groundwater contamination by nitrate from land-based sludge disposal was evaluated. A controlled large-lysimeter experiment was set up to monitor movement of nitrate through soil. Four large lysimeters of 900 mm length were packed with Manawatu fine sandy loam (a Dystric Fluventric Eutrochrept), on top of which 200 mm of municipal sewage sludge was applied. One of the lysimeters was planted with pasture (Lolium perenne and Festuca arundacea), one with a willow tree (Salix sp. ‘Tongoio’), another with a poplar tree (Populus sp. ‘Kawa’), and one was left bare. Bromide was used as a conservative tracer. Movement of bromide and nitrate was analysed in the effluent from the base of the lysimeters.The processes of water and nutrient transport were modelled using a mechanistic scheme based on Richards’ equation for water transport and the convection–dispersion equation (CDE) for nutrient transport. These equations were both linked to a sink term for plant uptake. The model simulated well the transport of water and movement of bromide in the four different lysimeters. The agreement between measured and simulated nitrate leaching was also reasonable considering the simplified model. Uptake of nitrogen by trees reduced the quantity of nitrogen available for leaching. The model could aid development of sustainable management of land-based sewage sludge disposal in terms of nitrate leaching. The next step will be to further develop the model for heavy metal movement, as heavy metals are common co-contaminants of sewage sludge.     

Current and Future Outlook of Dredged and Sewage Sludge Materials in Agriculture and Environment (3 pp)

-  In the late 1960’s there was an increasing realization in the U.S.A. and other parts of the world, especially in Europe of the potential problems associated with the disposal of spoil and sewage sludge materials. While insufficient information was available to determine potential adverse effects of disposal on land, many people including those in the scientific community had articulated their objections on the use of these materials in agriculture because data do not provide adequate environmental protection information. In many cases, site-specific geochemical and biological factors are typically excluded from the decision process (Wenning and Woltering 2001). Because of continued studies and far-reaching research during the last 40 years on the environmental effects of dredged and sludge materials, the scientific community and regulatory agencies in the U.S.A. are now in a much better position to appraise the environmental and possible agricultural impacts connected with the disposal of dredged and sludge materials by diverse disposal methods.     

Some investigations into the behavior of pentabromodiphenyl ether (PeBDE) in soils

Pentabromodiphenyl ethers (PeBDEs) are components of brominated flame retardants which have been detected in various environmental media (waste water, sewage sludge, sediments, and aquatic biota). They are ”?priority pollutants”. Sewage sludge from 20 different sewage treatment plants under summer and winter conditions showed PeBDE levels in primary sludge of up to 70 μg kg^—1 with a dominant range of 5—20 μg kg^—1. To insure a safe sludge use in agriculture, sorption, mobility, and dissipation experiments using soil substrates were conducted. PeBDE was bound strongly to organic matter (K_oc = 125,000) while K_d values after FREUNDLICH of about 90 and 700 were obtained for clay and sand, respectively, and of 45,000 for humus. Less than 0.001 % was found in eluates from laboratory lysimeters, and about 91 % remained at a depth of 0—3 cm. Thus PeBDE has a low mobility. In the indicative dissipation tests, the recovery rate after 3 weeks was about 50 %, and about 20—25 % was still detectable after 8 weeks. PeBDE proved to be less persistent than previously assumed. A formation of bound residues is presumed to be likely. Only a small difference was found between aerobic and anaerobic dissipation. The strong fixation in soil suggests a need to clarify whether PeBDE accumulates in soil.