Ultrasonic reduction of excess sludge from activated sludge system II: urban sewage treatment

Previous study showed that sonication was effective to reduce waste activated sludge (WAS) using artificial wastewater. This paper confirms the viability and evaluates the performance of this method in practical wastewater treatment using urban sewage without temperature control. The results showed that sonication significantly lowered the WAS and biomass synthesis, and greatly enhanced the mineralization of sewage organics. The optimal specific energy for sludge lysis was 20.0k Wh/kg DS. Further energy-increase had little benefit on WAS reduction. When the specific energy was 20.0kWh/kgDS and the sludge recycle ratio was 0.007, the WAS decreased by 54%, the biomass synthesis abated by 59%, and the sewage mineralization ratio increased from 31% to 58%. The effluent COD and nitrogen were stable but phosphorus was higher than that of the control bioreactor. The COD removal was lower but the WAS reduction was higher for urban sewage than for artificial wastewater. The accumulation pattern of heavy metals in sludge was greatly alternated by the sonication-cryptic growth; and different metals behaved differently. The sludge Ni concentration increased by 141% while As decreased by 53%.     

污水厂脱水污泥制吸附剂及脱除H2S效能研究

采用热解炭化法制备了一系列污泥吸附剂,优化制备工艺,利用扫描电镜(SEM)、比表面积和孔径分析等技术对污泥吸附剂的结构进行了表征,并研究了脱除H2S效能。结果表明,活化温度、活化时间和固液比等因素均对污泥吸附剂的碘吸附值产生影响。当活化温度为550℃、活化时间为2.0h、固液比为1∶2时所制备材料(SA)的碘吸附值最高,为493.12mg/g;制备的SA具有较好的脱除H2S效能,能满足精脱硫的要求,当空速为4600h-1时,SA的除臭时间可达48min;此外SA中含有的多种金属元素,平均孔径为3.4nm,这些性质均有利于H2S的吸附脱除。     

Metal sorption on soils as affected by the dissolved organic matter in sewage sludge and the relative calculation of sewage sludge application

To evaluate the influences of sewage sludge-derived organic matters on metal sorption and on the resultant sludge loading estimates, a batch experiment was conducted to compare the sorption of Ni, Cu and Pb in sewage sludge filtrates (1:20 sewage sludge to water) on eight soils and the adsorption of metals in a reference solution which had the same matrix as the sewage sludge filtrate except dissolved organic material (henceforth referred to as reference solution). Metal sorption could be well fitted by linear isotherm and the dissolved organic matter in sludge significantly depressed the sorption (p<0.01). The main factor controlling sorption of Ni on different soils was dominated by soil cation exchange capacity (CEC) and sorption of Cu and Pb was by soil organic matter (SOM). The parameters obtained from the sorption isotherm equations were then used to estimate sludge loadings into the soils. When the sorption parameters derived from the reference solution were used for calculation, that is the effect of dissolved organic matter was not considered, the calculated safe application rates are approximately 47.8, 51.4, 34.2, 31.3, 21.7, 46.3, 187.1 and 27.6 t-sludge/ha for the Beijing, Jiangxi, Xiamen, Jilin, Guangdong, Wuhan, Gansu and Xinjiang soils, respectively. However, when the sorption parameters derived from the dissolved organo-metallic complexes are used for calculation, the corresponding application rates are reduced to approximately 6.0, 3.4, 1.9, 10.0, 6.3, 3.6, 7.3 and 3.5 t-sludge/ha, respectively. By this study we can get a conclusion that the effect of sewage sludge derived dissolved organic matter on heavy metal sorption and soil properties should be considered in the course of regulating the safe application rates of sewage sludge to soil.     

Investigation of sewage sludge stabilization potential by the addition of fly ash and lime

The aim of this work was the examination of stabilization potential of sewage sludge by the addition of fly ash and/or lime and the investigation of the effect of stabilization time on the properties of produced mixtures. Five samples were prepared by mixing fly ash, sewage sludge and lime in various ratios and the mixtures were stabilized for a period of 35 d. The addition of alkaline agents resulted in the increase of sample pH up to 12, the increase of total solids content to about 50% and the reduction of the organic fraction of the solids. The produced samples presented inhibition effects to seed germination and root length growth of three higher plants (one monocotyl and two dicotyls); however, samples with high sludge content resulted in negligible seed germination inhibition at prolonged stabilization times. The standard TCLP leaching procedure was applied in all the produced samples in order to evaluate the extraction potential of certain metallic elements; the content of metals in the eluates was varied, depending upon their speciation and form. Eluates presented significant inhibition to the marine photobacterium Vibrio fischeri bioluminescence, while the lowest inhibition was detected for the samples containing higher sludge content. These samples potentially could be applied as soil amendment, offering an efficient method for the combined utilization of two different solid wastes; however, low dosages of fly ash should be used for the production of a stabilized material presenting negligible effects with respect to its phytotoxic and ecotoxic properties.     

Stabilization treatment of soft subgrade soil by sewage sludge ash and cement

In this study, incinerated sewage sludge ash (ISSA) is mixed with cement in a fixed ratio of 4:1 for use as a stabilizer to improve the strength of soft, cohesive, subgrade soil. Five different ratios (in wt%: 0%, 2%, 4%, 8%, and 16%) of ISSA/cement admixture are mixed with cohesive soil to make soil samples. In order to understand the influences of admixtures on the soil properties, tests of the pH value, Atterberg limits, compaction, California bearing ratio (CBR), unconfined compressive strength, and triaxial compression were performed on those samples. The study shows that the unconfined compressive strength of specimens with the ISSA/cement addition was improved to approximately 3-7 times better than that of the untreated soil; furthermore, the swelling behavior was also effectively reduced as much as 10-60% for those samples. In some samples, the ISSA/cement additive improved the CBR values by up to 30 times that of untreated soil. This suggests that ISSA/cement has many potential applications in the field of geotechnical engineering.     

Sugarcane bagasses sewage sludge compost as a plant growth substrate and an option for waste management

The possible utilization of sugarcane bagasses sewage sludge-based compost (BSC) as a substitution for widely using expensive peat in growth media for a horticultural crop, lettuce (Lactuca sativa L.), was evaluated. Five different treatments having different percentages of BSC and peat were established. Percentages of BSC addition to peat were 0, 10, 25, 40, and 60%?v/v, respectively. Physical and chemical characteristics of different growth media were undertaken. Plant growth parameters and nutrient composition of lettuce plants were determined. In general, the proposed growing media created with peat and BSC had adequate physical and chemical properties and notable contents of plant nutrients, mainly P, K, Ca, and Mg. Moreover, BSC addition to peat enhanced the nutrient content in lettuce plants compared to plants grown in peat-only substrate. The highest increases of growth and yield parameters were obtained in the treatment having BSC and peat at 25 and 75% of the total volume, respectively. The shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight obtained from the media having BSC and peat at 25 and 75% were increased by 53.25, 43.32, 36.27, and 56.88%, respectively, compared to peat control. In addition, the mixture with the most BSC (60%) gave the greatest contents of K, Mg, Ca, Cu, Zn, Cr, and Pb. Trace element concentrations in plant tissues grown in media with BSC and peat were far below than the ranges considered phytotoxic for plants. These results indicate that these BSC-based media is a viable alternative to expensive peat for cultivation of lettuce.     

Treatment of sewage sludge using electrokinetic geosynthetics

The treatment and disposal of sewage sludge is one of the most problematical issues affecting wastewater treatment in the developed world. The traditional outlets for sewage sludge are to spread it on agricultural land, or to form a cake for deposit to landfill or incineration. In order to create a sludge cake, water must be removed. Existing dewatering technology based on pressure can only remove a very limited amount of this water because of the way in which water is bound to the sludge particles or flocs. Several researchers have shown that electrokinetic dewatering of sludge is more efficient than conventional hydraulically driven methods. This involves the application of a dc voltage across the sludge, driving water under an electrical gradient from positive (anode) electrode to negative (cathode) electrode. However, there have been several reasons why this technique has not been adopted in practice, not least because the, normally metallic, anode rapidly dissolves due to the acidic environment created by the electrolysis of water. This paper will describe experimentation using electrokinetic geosynthetics (EKG): polymer-based materials containing conducting elements. These have been used to minimise the problem of electrode corrosion and create a sludge treatment system that can produce dry solids contents in excess of 30%. It will suggest different options for the treatment of sludges both in situ in sludge lagoons and windrows, and ex situ as a treatment process.     

Stabilization of primary sewage sludge during vermicomposting

In India, over the last few decades, there has been a remarkable increase in sewage sludge production due to population increase and unplanned urbanization. The aim of the present study was to investigate the ability of an epigeic earthworm Eisenia foetida to transform primary sewage sludge (PSS) amended with cow dung (CD) into value added product, i.e., vermicompost in laboratory scale experiments. Two approaches investigated in the study were: (1) evaluation of vermistabilization of PSS and CD mixtures after 15 weeks in terms of fertilizer quality of the products and; (2) growth and reproduction of Eisenia foetida up to 11 weeks in different vermireactors. In all the PSS and CD mixtures, a decrease in pH, TOC and C:N ratio, but increase in EC, TKN, TK and TP was recorded. The heavy metals' content in the vermicomposts was higher than initial mixtures. Maximum worm biomass was attained in 10% PSS+90% CD mixture while, the worm growth rate was highest in 30% PSS+70% CD feed mixture. It was inferred from the study that addition of 30-40% of PSS with CD had no adverse effect on the fertilizer value of the vermicompost as well as growth of Eisenia foetida. The results indicated that PSS could be converted into good quality manure by vermicomposting if mixed in appropriate ratio (30-40%) with cow dung.     

Effect of milling and acid washing on the pozzolanic activity of incinerator sewage sludge ash

Incinerator sewage sludge ash (ISSA) is a problematic waste that contains significant levels of phosphates, primarily in the form of whitlockite (Ca₃(PO₄)₂). Phosphate is a valuable finite resource, and a number of studies have shown that it can be extracted from ISSA by acid washing. This produces an acid washed residue that has potential to be used in construction products. The effects of milling and acid washing on the pozzolanic activity of ISSA have been evaluated using the strength activity index (SAI) test and the Frattini test. Coal fly ash (FA), metakaolin (MK) and quartz sand were also tested for comparison. Milling improved the pozzolanic activity of FA and ISSA according to both the SAI and Frattini tests. If ISSA is acid washed to recover phosphate, the process is likely to produce an acid insoluble material with little or no pozzolanic activity. The Frattini test is considered a more suitable method for directly assessing pozzolanic activity as a range of factors can affect SAI test results.     

Application of radiation technology to sewage sludge processing: a review

Sewage sludge is unwanted residual solid wastes generated in wastewater treatment and its management is one of the most critical environmental issues of today. The treatment and disposal of sludge contribute a considerable proportion of the cost for running a wastewater treatment plant. The increasing amount of sewage sludge and more and more legislative regulation of its disposal have stimulated the need for developing new technologies to process sewage sludge efficiently and economically. One ideal consideration is to recycle it after proper treatment. Radiation technology is regarded to be a promising alternative for its high efficiency in pathogen inactivation, organic pollutants oxidation, odor nuisance elimination and some other characteristics enhancement, which will facilitate the down-stream process of sludge treatment and disposal. Here we present a brief review of application of radiation technology on sewage sludge processing. Some basic information of two currently available irradiation systems and fundamental radiation chemistry are introduced firstly; then the world-wide application of this promising technology is reviewed; various effects of radiation on sludge is discussed in detail; and some concluding remarks are given and some future directions are also proposed.     

Preparation of single-crystalline nickel nanoflowers and their potential application in sewage treatment

Control of the nucleation and growth rate by H₂O₂ and NaOH provides a facile route to harvest nickel nanoflowers. The choice of NaOH and ethylene glycol (EG) plays the important role in the formation of Ni nanoflowers; while the addition of H₂O₂ is another key role for the preparation of uniform Ni nanoflowers. HRTEM and SEAD patterns show that the Ni nanoflowers are single-crystal and grow along the [200] direction. The magnetic measurement demonstrated that the Ni nanoflowers presented ferromagnetic properties. Furthermore, Ni nanoflowers show potential utilization for the removal of dyes in a wastewater treatment process.     

Transformation of heavy metal forms during sewage sludge bioleaching

The transformation of heavy metal forms during sewage sludge bioleaching with elemental sulfur as substrate was investigated. The sequential selective extraction procedure was an effective way to reflect the variation in heavy metal forms. The exchangeable form of Cu, Pb and Zn after bioleaching accounted for 81.6, 40.2 and 75.8%, respectively. Cu at initial sludge mainly existed as sulfide precipitate form, most of which turned to exchangeable form during bioleaching, and was solubilized mostly by direct mechanism. The original forms of Pb and Zn were mainly carbonate precipitate and organically bound. Most of the carbonate precipitate Pb transformed into exchangeable form but a little of organically bound Pb. Pb was dissolved from the sludge due to transformation of carbonate precipitated and sulfide precipitated to exchangeable form by cooperation of both direct and indirect mechanisms. A majority of exchangeable Zn was transformed from organically bound and carbonate precipitated forms, and the bioleaching mechanism of Zn was mainly indirect. After bioleaching, the sewage sludge could be applied to land more safely because the heavy metals mainly existed in stable forms. The exchangeable Cu and Pb achieved an obvious increase at pH about 2, while exchangeable Zn showed higher percentage at pH about 3. The transformation of chemical forms for Cu had good relationship with ORP during bioleaching, but Zn was not influenced by ORP of sludge, which appeared to have high bioleaching efficiency at ORP less than 200 mV.     

Ex-situ bioremediation of polycyclic aromatic hydrocarbons in sewage sludge

Polycyclic aromatic hydrocarbons (PAH) are regarded as environmental pollutants. A promising approach to reduce PAH pollution is based on the implementation of the natural potential of some microorganisms to utilize hydrocarbons. In this study Proteiniphilum acetatigenes was used for bioaugmentation of sewage sludge to improve the PAH removal. Bioaugmentation experiments were performed in parallel semi-continuously fed reactors started up with digested primary and secondary sludge. Three bioaugmentation approaches were investigated: A1, addition of bacteria once during starting up; A2, addition of bacteria at the beginning and then every 2nd day and A3, addition of encapsulated bacteria once during starting up. Removal of PAH was found to be both biotic and abiotic. All three approaches had a positive effect of the biological removal of PAH. Highest biological removal of individual PAH (up to 80%) was observed using continuous addition (approach A2) of the bacteria to the reactors. In general, the effect of bioaugmentation was higher in the reactors fed with primary sludge compared to the reactors fed with mixed sludge. Bioaugmentation resulted in biological removal of low molecular weight PAH in the reactors fed with primary sludge using all three approaches while clear biological removal of the medium- and high molecular weight PAH only was observed if the bacteria were added continuously (approach A2).     

Mineralogy and leachability of gasified sewage sludge solid residues

Gasification of sewage sludge produces combustible gases as well as tar and a solid residue as by-products. This must be taken into account when determining the optimal thermal conditions for the gasification process. In this study, the influence of temperature, heating atmosphere and residence time on the characteristics of the gasified sewage sludge residues is investigated. ICP-AES analyses reveal that the major chemical elements in the char residues are phosphorus, calcium, iron and silicon. Heavy metals such as copper, zinc, chromium, nickel and lead are also present at relatively high levels - from 50 to more than 1000 mg/kg of dry matter. The major mineral phases' identification - before and after heating - as well as their morphology and approximate chemistry (XRD and SEM-EDX) demonstrate that a number of transformations take place during gasification. These are influenced by the reactor's temperature and the oxidative degree of its internal atmosphere. The copper-, zinc- and chromium-bearing phases are studied using chemometric tools, showing that the distribution of those metals among the mineral phases is considerably different. Finally, batch-leaching tests reveal that metals retained in the residue are significantly stabilized after thermal treatment to a higher or lower extent, depending on the thermal conditions applied.     

Impact of thermal treatment on metal in sewage sludge from the Psittalias wastewater treatment plant, Athens, Greece

This paper describes a laboratory study that examined the effect of thermal treatment at four different temperatures on the behavior of heavy metals in the anaerobically treated primary sludge from the Psittalias wastewater treatment plant. The sewage sludge was found to contain significant amounts of heavy metals (Cr, Cu, Fe, Ni, Pb and Zn). The metal form distribution in the sludge samples which was determining by the application of a sequential extraction procedure revealed that a significant portion of metals was embodied in the organic and reducible fractions. Treatment at 105, 250, 650 and 900 degrees C demonstrated significant conversions of the metals to a less mobile form as well as removal by vaporization. By applying sequential analysis, it was found that most of the metals were removed from the initial mobile phases to more stable ones. Also, significant amounts were transformed to the gaseous phase.     

Evaluation of electrokinetic removal of heavy metals from sewage sludge

The presence of heavy metals is one of the main obstacles for agricultural use of million tonnes of dewatered sewage sludge produced in wastewater treatment plants. Electrokinetic (EK) treatment can be applied to remove heavy metals from sludge. The aim of this study was to increase the efficiency of electrokinetic removal of heavy metals from dewatered sewage sludge. EK experiments were carried out with and without pH adjustment in cathode chamber of acidified sewage sludge. The selective sequential extraction (SSE) was used to determine the fractionation of heavy metals in sewage sludge. The mobility of heavy metals in sludge significantly increased after its acidification at pH 2.7 and followed the order: Ni, Zn, Cu, As, Cr, Pb. Removal efficiencies of heavy metals in the experiment with acidified sewage sludge and pH adjustment at cathode chamber at 2.0 were: 95% for Zn, 96% for Cu, 90% for Ni, 68% for Cr, 31% for As and 19% for Pb. The concentrations of Zn, Cu, Ni, Cr and Pb after EK treatment were below the United States Environmental Protection Agency limits for biosolids applied to agricultural land, forest, public contact sites or reclamation sites.     

Enhancing simultaneous electricity production and reduction of sewage sludge in two-chamber MFC by aerobic sludge digestion and sludge pretreatments

Batch tests were conducted to enhancing simultaneous electricity production and reduction of sewage sludge in two-chamber MFC by aerobic sludge digestion in cathode chamber and sludge pretreatments (sterilization and base pretreatment) prior to sludge addition to anode chamber, respectively. During the stable stage, The voltage outputs and power densities of MFC increased from 0.28-0.31 V to 17.3-21.2 mW/m(2) to 0.41-0.43 V and 36.8-40.1 mW/m(2), respectively, when aerobic sludge digestion occurred in the cathode chamber. When the sludge added to the anode chamber was sterilized or base pretreated, the voltage outputs and power densities of MFC increased from 0.30-0.32 V and 19.9-22.6 mW/m(2) (raw sludge) to 0.34-0.36 V and 25.5-28.6 mW/m(2) (sterilized sludge), 0.41-0.43 V and 37.1-40.8 mW/m(2) (base pretreated sludge), respectively. At the end of the test, the total suspended solids (TSS) and volatile suspended solids (VSS) reduction of sludge in the anode chambers increased from 33.9% and 36.8% to 34.5% and 38.7% with aerobic sludge digestion in the cathode chamber, respectively; while, those (TSS and VSS reduction) with sludge pretreatments prior to the sludge addition to the anode chambers increased from 25.1% and 22.8% (raw sludge) to 32.8% and 34.6% (sterilized sludge), and 25.5% and 26.7% (base pretreated sludge), respectively. The experimental results illuminated both aerobic sludge digestion in the cathode chamber and sludge pretreatments (sterilization and base pretreatment) prior to sludge addition to the anode chamber could enhance simultaneous electricity production from sludge and sludge reduction.     

膜分离技术在城市污泥减量化中的应用

随着城市污泥产量的持续增加,污泥减量化越来越受到重视.阐述了膜分离技术在减少剩余污泥产量及污泥浓缩和消化处理中的应用机制,总结了各种用于污泥减量化的膜分离技术的研究进展和优缺点,最后指出了膜分离技术在污泥减量化中应用的研究重点和方向.     

Interactions of NO2 with sewage sludge based composite adsorbents

Interactions of NO2 present in most air were analyzed at room temperature on composite sewage sludge-derived adsorbents. They consist of carbonaceous and inorganic phases with the majority of the latter. The adsorption capacity was evaluated using the dynamic breakthrough experiments. The materials before and after NO2 exposure were characterized using adsorption of nitrogen, thermal analysis and FTIR. The results showed differences in the surface activities of sludge-derived materials towards immobilization and reduction of nitric dioxide. Nitrates and nitrite are the main products of surface reactions. This is linked to the presence of active oxides and hydroxides, which are formed when the surface is exposed to water. The highest activity of the sample pyrolyzed at 650 degrees C is owing to the high content of those species formed as a result of decomposition of inorganic salts (likely chlorides, sulfates and phosphates) during thermal treatment. When sludge is pyrolyzed at 950 degrees C those oxides are engaged in stable mineral phases formed in solid-state reactions, which limits the surface activity towards NO2 retention. The reactivity of the high temperature pyrolyzed samples can be linked to the physical adsorption of water. In a water film nitrous and nitric acid can be formed and they can further react with inorganic and carbonaceous phases to the limited extent.