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The utilization of calcium carbide residue (CCR) to activate solid wastes can effectively promote sustainable development. This paper explores adding sodium carbonate (Na2CO3) to CCR activators to improve the early reactivity of alkali-activated materials (AAMs) made from sewage sludge ash (SSA). The research focuses on the effects of Na2CO3 on setting, hardening, mechanical strength, and environmental benefits. The findings indicate that Na2CO3 can shorten the paste' hardening time and significantly enhance the early mechanical properties. The introduction of Na2CO3 accelerates the consumption of CCR during the early phases and facilitates the formation of C-(N)-A-S-H gels. Meanwhile, it can significantly reduce the porosity and refine the pore structure. When the dosage reaches 8%, the total intruded pore volume of the sample decreases to 0.15 mL/g. This activation method reduces energy consumption, CO2 emissions, and costs by 69%, 50%, and over 90%, respectively, making it an efficient, eco-friendly approach to AAM production. [ABSTRACT FROM AUTHOR]

The disposal of fly ash (FA) from coal power plants polluting the air, soil, and groundwater is a major environmental concern. Phytoremediation to rehabilitate fly ash dumpsites is a promising alternative but has practical concerns about the disposal of harvested biomass. This study investigated the effect of supplementing fly ash with fresh sewage sludge (FSS), aged sewage sludge, food waste, and compost (COM) to enhance the phytoremediation potential of Napier grass and its subsequent utilization for ethanol production. The highest removal of Mn (1196.12 g ha−1) and Ni (128.06 g ha−1) from FA could be obtained when Napier is grown in the presence of FSS and inorganic fertilizer (NPK). In addition, the highest bioethanol yield (19.31 g L−1) was obtained from Napier grown in fly ash with COM + NPK, thus providing additional economic benefits aside from the remediation process. Given the significant levels of heavy metals present in the pulp and bio-slurry after ethanol production, further research is required in this area to determine the best ways to utilize this waste such as converting it into biochar. Using energy crops as a phytoremediation agent for fly ash dumpsites has the potential to remediate heavy metal contamination and provide additional economic benefits. Napier grass was able to tolerate high concentrations of heavy metals and yield high biomass in fly ash in the presence of organic amendments. The harvested biomass was successfully converted into substrate for bioethanol production using heavy metal-tolerant yeast. This is the first report on the production of ethanol from the phytoremediation biomass of Napier grass. [ABSTRACT FROM AUTHOR]

This paper highlights an innovative approach to address the environmental challenges associated with waste management and construction materials. The study presents a new technique for utilising treated sewage sludge in the production of eco-friendly geopolymer mortar. Sewage sludge is a byproduct generated from wastewater treatment plants that poses significant environmental issues due to its disposal problems. Geopolymer mortar, on the other hand, is a sustainable construction material that can be produced by activating industrial waste materials, such as fly ash, using alkaline activators. By integrating machine learning algorithms and data visualisation techniques, this study optimises the mix parameters of geopolymer mortar while simultaneously reducing the negative impact of sewage sludge disposal. The experimental results show that sewage sludge ash can replace fly ash and fine aggregate in 1:3 geopolymer mortar by up to 30% and 20%, respectively, without any toxic or heavy metal residues. The compressive and flexural strength of the sludge-based mortar were comparable to ordinary geopolymer mortar, while water absorption and drying shrinkage were similar to control specimens. This research offers a unique solution to promote sustainability in waste management and construction industry by utilising waste materials, including fly ash and treated sewage sludge, for geopolymer production. [ABSTRACT FROM AUTHOR]

This study uses a new approach for the recycling of plant nutrients by co-digesting sewage sludge with fly ash from a wood combustion. Sewage sludge and fly ash both are enriched with nutrients of the wastewater resp. wood, which makes these products an enhanced source for recycled fertilizers. The effects of the ash addition to the anaerobic digestion are studied in several lab scale experiments including effects on the gas production and microbial activity. Following that, the fertilizing qualities of the digestate are evaluated by plant growth experiments. The results show that the fertilizing qualities of the digested sludge were improved by the ash addition. Next to this, gas production results show that the methane production was not affected by the ash addition, while the total gas release was reduced. The sulphur addition by the ash stimulated sulphate reducing bacteria. The sulphate reducing bacteria did not markedly inhibit the methanogens. [ABSTRACT FROM AUTHOR]

Rapid urbanization has resulted in the production of large quantities of sewage sludge over worldwide. The disposal of sewage sludge in landfills or open areas is not considered as an environmentally friendly solution. Therefore, the use of sewage sludge as ash can provide a better solution in geotechnical applications. Keeping this in view, this study investigates the possibility of using sewage sludge ash (SSA) to improve the geotechnical properties of soft clay soil. The sewage sludge ash (SSA) is attained by burning the sludge for 2 h at 900°C. The tests conducted on the clayey soil are specific gravity, standard Proctor test, sieve analysis, Atterberg limits, CBR test and unconfined compression test. Three curing times were used for the untreated soils and soils treated with sewage sludge ash (SSA) which are 3 days, 14 days and 28 days. The sewage sludge ash (SSA) was mixed with the soil at different percentages by weight of the soil at 10%, 15% and 20% of dry soil weight. The results showed that the sludge ash increases the unconfined compressive strength of the soft soil at 3, 14, 28-day curing time. The bearing capacity of the soil decreases after adding SSA at the first, but curing time led to improve the bearing capacity of clayey soil after adding SSA and the percentage of SSA of 10% gave the optimum value of CBR. The results indicated that a better performance of the unconfined shear strength was obtained at 28-day curing time. The findings of this research indicate that sewage sludge ash (SSA) can be used to improve the soft clayey soil and further reduce the environmental risks associated with this substantial.Implications: Rapid urbanization has resulted in the production of large quantities of sewage sludge over worldwide. The disposal of sewage sludge in landfills or open areas is not considered as an environmentally friendly solution. Therefore, the use of sewage sludge as ash can provide a better solution in geotechnical applications. Keeping this in view, this study investigates the possibility of using sewage sludge ash (SSA) to improve geotechnical properties of soft clay soil. In this paper, Sewage Sludge Ash (SSA) is recycled as a new type of chemical addition to soft clay soil and used as a stabilizer to improve a clayey soil. This study proposes that a percent of the total amount of clay to be reinforced is replaced with sewage sludge ash (sewage sludge ash plus soil) in order to achieve the need of improvement in the geotechnical properties of clayey soil and make use of industrial wastes. The sewage sludge ash (SSA) is attained by burning the sludge for 2 h at 900°C. The tests conducted on the clayey soil are specific gravity, standard Proctor test, sieve analysis, Atterberg limits, CBR test, and unconfined compression test. Three curing times were used for the untreated soils and soils treated with sewage sludge ash (SSA) which are 3 days, 14 days, and 28 days. The sludge ash (SSA) was mixed with the soil at different percentages by weight of the soil at 10%, 15%, and 20% of dry soil weight. The results showed that the sludge ash increases the unconfined compression strength of the soft soil at 3, 14, 28-day curing time. The bearing capacity of the soil decreases after adding SSA at the first, but curing time led to improve the bearing capacity of clayey soil after adding SSA and the percentage of SSA of 10% gave the optimum value of CBR. The results indicated that a better performance of the unconfined shear strength was obtained at 28-day curing time. The findings of this research indicate that sewage sludge ash (SSA) can be used to improve the soft clayey soil and further reduce the environmental risks associated with this substantial. [ABSTRACT FROM AUTHOR]

Incinerated sewage sludge ash (ISSA) is produced worldwide where incineration is used to manage sewage sludge. ISSA contains significant amounts of phosphorus (P) with high recovery potential, and may contribute to mitigate the global P supply problem. This study reviews P transformation in sewage sludge incineration, the characteristics of the resultant ISSA and processes for P recovery from ISSA focusing on wet-extraction methods due to their greater feasibility. The major drawback of the wet-extraction method is the co-dissolution of metal(loid)s. Hence, purification of the P-extract is necessary to produce a P fertilizer. Based on the analysis, three recommendations are made for further studies. One is optimizing the extraction process to produce a P-extract with a high content of P and low contents of impurities. The second is to develop a plant-available adsorption media, which can selectively adsorb P from the acid-extract of ISSA making the P-laden media as P fertilizers directly. The third is to form a high-purity P product that would be cost-competitive and attractive for use in diverse sectors. Finally, since the criteria for recovered phosphate fertilizer is incomplete, the agronomic effectiveness of newly produced P fertilizer from ISSA should be evaluated prior to large scale applications. [ABSTRACT FROM AUTHOR]

Developing beneficial applications for sewage sludge is a key challenge in many countries, given the amount of sludge generated and the disposal or recycling options currently available. Sewage sludge from the wastewater treatment plant at Koprivnica in Croatia has been treated using MID-MIX® technology that involves the addition of Ca(OH)2 and CaO to dewatered sludge. This produces a low-density non-hazardous white-grey powder. The treated sewage sludge has been heated to 800, 900 and 1000 °C to form MID-MIX® treated sewage sludge ash with reduced organic content. MID-MIX® treated sewage sludge and ash have been used to replace 10 and 20% of cement in mortar and concrete samples. The addition of MID-MIX® treated sewage sludge causes a significant increase in void content which reduces the mechanical properties and durability of mortar and concrete samples. However, replacement of cement by MID-MIX® ash did not significantly affect the strength, water penetration or gas permeability compared to control samples. Leaching tests on MID-MIX® powder, MID-MIX® ash and mortar samples produced low levels of heavy metal release. The research shows that thermally processed MID-MIX® treated sewage sludge produces an ash product that has potential to be beneficially used in cementitious materials for selected applications. [ABSTRACT FROM AUTHOR]

The aim of the present research was to investigate the influence of different biomasses and sewage sludge ash (at 650°C for 1000 h and 2000 h, respectively) on the surface of weld cladded (Cold Metal Transfer technique, CMT) stainless steels 309 and 310. The biomass ashes were rich in K2O, CaO, SiO2, whereas sewage sludge ash in P2O5, CaO, Fe2O3, and SiO2. Characterization of the stainless steel cross-section and surface after the corrosion process inducted by the presence of ash were carried out by scanning electron microscopy (SEM) with EDAX analysis. Phase analysis of corrosion products was made by X-ray diffraction (XRD). Chromium, nickel, and iron oxides were the main oxides which occurred after the corrosion test. It has been proved that biomass ashes have the corrosive properties (because of their chemical composition) and are more aggressive than the sewage sludge ash for that kind of materials. [ABSTRACT FROM AUTHOR]

In this work, we reported results obtained during experimental tests to introduce a new approach to the treatment of dredging sludge polluted by mercury. A slurry of dredging sludge was treated by cationic exchange procedures both at ambient temperature and distilled at 393K with the aid of some different exchange salts: three inorganic (NaCl, CaCl2, and CaI2) and two organic Tetrabutylammonium chloride [(C4H9)4NCl] and Ethyl Viologen diiodide (1,1′-Dietil-4,4′-bipyridinium diiodide) [C14H18I2N2], having different cationic exchangeable part and different molecular weights. A similar (15% w/w) solution was used to treat mercury-polluted sludge considering 2, 24, and 48 h of reaction time. The removal efficiencies of the inorganic/low molecular weight monovalent salts were minimal at the tested temperatures, while higher removal was reached when CaI2 and Viol-I2 were used at ambient temperature with maximum treatment efficiencies over 70% in 48 h treatment. A recovery/reuse of the exchanging solutions was also tested finding good recovery potential of the salt slurry. [ABSTRACT FROM AUTHOR]

Sewage sludge ash (SSA) produced by municipal sludge can be used as a modified additive for clay liner, and improves the working performance of landfill clay liner in contact with leachate. Under the action of landfill leachate, the permeability, shear strength, phase composition, and pore structure of the modified clay are investigated through the flexible wall permeability test, triaxial shear test, thermal gravimetric and differential thermal analysis, and low-temperature nitrogen adsorption test, respectively. The hydraulic conductivity of the modified clay containing 0-5% SSA is in the range of 3.94 × 10-8-1.16 × 10-7 cm/s, and the pollutant concentration of the sample without SSA was higher than others. The shear strength of the modified clay is more than that of the traditional clay liner, the cohesion rate of modified clay increases from 32.5 to 199.91 kPa, and the internal friction angle decreases from 32.5° to 15.6°. Furthermore, the weight loss rates of the samples are 15.69%, 17.92%, 18.06%, and 20.68%, respectively, when the SSA content increases from 0% to 5%. The total pore volume and average pore diameter of the modified clay decrease with the increase in the SSA content, respectively. However, the specific area of the modified clay increases with the increase in the SSA content. [ABSTRACT FROM AUTHOR]

Anaerobic digestate of piggery wastewater (ADPW) contains high concentrations of ammonia and phosphorus with unbalanced molar ratio. Thus, ammonia remains at a high level even after phosphorus is completely removed through struvite formation. In this study, both ammonia and phosphorus were recovered by adding leachate of sewage sludge ash (SSA) into ADPW. It was demonstrated that 11,600 mg L-1 of total phosphorus and 7266.7 mg L-1 of PO3- 4 -P were extracted from SSA by using sulfuric acid at the H2SO4/SSA mass ratio of 0.35. ADPW and the leachate of SSA were mixed at the volumetric ratio of 1:1.29, and then struvite was formed at the molar ratio of 1.2 (Mg2+):1.0 (PO3-4 -P):1.0 (NH3-N). Removal efficiencies of ammonia and phosphorus were 91.95% and 99.65%, respectively. The obtained struvite was analyzed by various methods and was found to meet the Korean fertilizer standards, except for copper. [ABSTRACT FROM AUTHOR]

There is an inadequate attempt to make a decision on the accuracy and reliability of the effectively usable dosage rates of sewage sludge ash (SSA) for replacement and improvement of coarse-grained soil. This study introduces an investigation on the effectively usable dosages of SSA for subbase construction by using factorial experimental approach and effect size estimation. California bearing ratio (CBR) tests have been carried out to measure the parameters of CBR value, energy absorption capacity (Ed) and ultimate bearing capacity (qu) of the soil + SSA mixtures for which proportions were 0, 5, 10, 15, 20, 30, 40, 50 and 60% by dry weight of the mixture. The effectively usable dosages of SSA for both improvement and substitute in highway construction, based on the foregoing parameters, have been assessed essentially using multiple comparison tests and effect size parameters (omega-squared, eta-squared and Cohen’sd). The results of statistical analysis demonstrate that while there is an insignificantly variation (increase or decrease) (p > .05 and Cohen’sd ≤ .41) at the dosage rates of 5 and 15% for CBR, 15% forEdand 5, 20, 30 and 40% forqu, there is a significant decrease (p ≤ .05 and Cohen’sd > 2.7) in the values of CBR,Edandqudue to the addition of SSA at the dosages of 50, 50 and 60%, respectively. Accordingly, it is suggested that SSA be introduced into sandy soil for improvement or replacement at the dosage rates less than 50% in the stabilisation applications. From the statistical analysis performed here, it is also found that multiple comparison tests and effect size estimates compare well in the decision-making. [ABSTRACT FROM AUTHOR]

Applying sewage sludge ash (SSA) to produce reclaimed tiles is a promising recycling technology in resolving the increasing sludge wastes from wastewater treatment. However, performance of such reclaimed tiles is inferior to that of original ceramic tiles. Many researchers have therefore tried adding various industrial by-products to improve reclaimed tile properties. In this study, multiple materials including waste glass and waste foundry sand (WFS) were added in an attempt to improve physical and mechanical properties of reclaimed tiles with SSA. Samples with various combinations of clay, WFS, waste glass and SSA were made with three kiln temperatures of 1000°C, 1050°C, and 1100°C. A series of tests on the samples were next conducted. Test results showed that waste glass had positive effects on bending strength, water absorption and weight loss on ignition, while WFS contributed the most in reducing shrinkage, but could decrease the tile bending strength when large amount was added at a high kiln temperature. This study suggested that a combination of WFS from 10% to 15%, waste glass from 15% to 20%, SSA at 10% at a kiln temperature between 1000°C and 1050°C could result in quality reclaimed tiles with a balanced performance. [ABSTRACT FROM PUBLISHER]

This study explored the suitability of using sewage sludge ash (SSA) and mixed-colored glass powder (MGP) as construction materials in cement mortars. Positive findings from this study may help promote the recycling of waste SSA and MGP in construction works. The results indicated that the SSA decreased while MGP improved the mortar workability. The SSA exhibited very low pozzolanic activity, but the cement mortar prepared with 20% SSA yielded strength values slightly superior to those of the glass mortars due to its water absorption ability. MGP can serve as a pozzolan and when 20% of cement was replaced by MGP, apparent compressive strength gains were found at later curing ages. The SSA could be used to mitigate ASR expansion while the MGP was superior in resisting drying shrinkage. [ABSTRACT FROM PUBLISHER]

The kinetics of batch fermentation of 13 extracellular polymeric substances (EPS) producing bacterial strains (9Bacillus, 2Serratiaand 2Yersinia) were carried out using sterilized sludge as a raw material. The most ofBacillus(µmax: 0.11–0.27 h−1),Serratia(µmax: 0.23–0.27 h−1) andYersinia(µmax: 0.18–0.19 h−1) strains had capability to grow and produce EPS (1.36–2.12 g/L) in the sterilized sludge. In general, EPS production was mixed growth associated for all the bacterial strains cultivated independently.Bacillussp. 7,Serratiasp. 2 andYersiniasp. 2 produced higher concentration (1.95–2.12 g/L) of EPS than the other remaining bacterial strains. Protein and carbohydrate contents of EPS remained constant during fermentation. Broth EPS (B-EPS) exhibited high kaolin flocculation activity (≥75%) in most of the cases exceptBacillussp. 1,Bacillussp. 5 andBacillussp. 9, respectively. In general, high flocculation activities (FAs) (≥75%), were attained using 1.31–1.70 mg B-EPS/g kaolin, 0.45–0.97 mg protein/g kaolin and 0.11–0.21 mg carbohydrates/g kaolin. The study suggests that further systematic exploration is required for optimizing the process of EPS production. EPS produced in the sludge can potentially be used for different water and wastewater treatments. [ABSTRACT FROM PUBLISHER]

In recent years, sewer systems and wastewater treatment plants have become important in developing countries. Consequently, the amount of sewage sludge produced by these countries has been gradually increasing, and determining how to properly recycle this sludge is becoming an important topic for researchers. In this study, to expand the recyclability of sewage sludge ash (SSA) in engineering applications, two types of nano-aluminium oxides (Al2O3), MC2A and MC2R, were added to SSA/cement paste and mortar specimens. The MC2R type (γ phase) had a smaller particle size and larger specific surface area than the MC2A type (α phase). The results indicate that the addition of nano-Al2O3to SSA/cement paste can effectively improve the hydration products of the paste. Moreover, the amount of hydration products increased as the amount of nano-Al2O3added to the SSA/cement paste increased. The test results indicate that MC2A nano-Al2O3can more uniformly distribute in the paste body and improve the hydration of cement than MC2R nano-Al2O3. Thus, more calcium-silicate-hydrate (C-S-H) gel and calcium aluminate hydrate (C-A-H) salts were produced, and the strength of the specimens was improved. This study suggests that MC2A nano-Al2O3is preferable to MC2R nano-Al2O3for SSA/cement specimen applications. [ABSTRACT FROM PUBLISHER]

The impact of carbon source variation on the physical and chemical characteristics of aerobic granular sludge and its biological nutrient (nitrogen and phosphorus) removal performance was investigated. Two identical sequencing batch reactors, R1 and R2, were set up. Granular biomass was cultivated to maturity using acetate-based synthetic wastewater. After mature granules in both reactors with simultaneous chemical oxygen demand (COD), ammonium and phosphorus removal capability were achieved, the feed of R2 was changed to municipal wastewater and R1 was continued on synthetic feed as control. Biological phosphorus removal was completely inhibited in R2 due to lack of readily biodegradable COD; however, the biomass maintained high ammonium and COD removal efficiencies. The disintegration of the granules in R2 occurred during the first two weeks after the change of feed, but it did not have significant impacts on settling properties of the sludge. Re-granulation of the biomass in R2 was then observed within 30 d after granules’ disintegration when the biomass acclimated to the new substrate. The granular biomass in R1 and R2 maintained a Sludge Volume Index close to 60 and 47 mL g−1, respectively, during the experimental period. It was concluded that changing the carbon source from readily biodegradable acetate to the more complex ones present in municipal wastewater did not have significant impacts on aerobic granular sludge characteristics; it particularly did not affect its settling properties. However, sufficient readily biodegradable carbon would have to be provided to maintain simultaneous biological nitrate and phosphorus removal. [ABSTRACT FROM PUBLISHER]

A proven bioevaporation process was used to treat food waste (FW) by mixing ground FW with biodried sludge (BS). Organic loading (OL), moisture content (MC), and air flow rate (Qg) showed significant influences on FW bioevaporation performance. Single-parameter experiments for MC andQgwere conducted and ranges were determined to be 55–67 wt% and 0.04–0.14 m3/kg TSmixture · h, respectively. In order to optimize the FW bioevaporation process, a central composite design (CCD) and response surface method (RSM) were applied over the preselected ranges of OL (0.00–0.16 kg VSFW/kg TSBS), MC (50.91–71.09 wt%), andQg(0.01–0.17 m3/kg TSmixture · h). The results indicated that OL of 0.06 kg VSFW/kg TSBS, MC of 59.2 wt%, andQgof 0.09 m3/kg TSmixture · h were the optimal conditions for the FW bioevaporation process. Water evaporation of 123.1% and VS degradation of 108.4% were obtained under these estimated optimal conditions. [ABSTRACT FROM PUBLISHER]

Digital image analysis has been intensively developed over the last two decades including its application to describe morphology of activated sludge flocs. However, only few studies concerned the variation of flocs morphology with respect to the operational conditions, particularly oxido-reductive conditions, in a full-scale wastewater treatment plant (WWTP). In this work, morphology of activated sludge flocs was monitored over one year in two different full-scale WWTPs. The main aim of this study was to find the relationship between the operational parameters and morphology of sludge flocs. Simultaneously, the variations in floc size along activated sludge chamber were studied with respect to the oxido-reductive conditions. It was found that the sludge loading rate was one of the most important operational parameters influencing floc size. It was estimated that its values higher than 0.1 kg BOD5 kg TS−1 d−1contributed to the decrease in floc size. Also, the oxido-reductive conditions influenced the floc size. It was statistically proved that flocs from the anaerobic zone were usually smaller than flocs from the anoxic or aerobic zones. Distribution of floc size in a full-scale WWTP usually could be described by a log-normal model. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential element for all life on earth. However, natural P resources (phosphate rock) are depleting. The authors describe the current situation and a forecast for future phosphate production and reserves. The current depletion of phosphate reserves and the increasingly stringent discharge regulations have led to the development of various P-recovery techniques from wastewater. Existing full-scale P-recovery techniques from the liquid phase, sludge phase, and sludge ash are reviewed. Although the full-scale P-recovery techniques have been shown to be technologically feasible, the economical feasibility, legislation and national policies are the major reasons why these techniques are not yet operational worldwide. [ABSTRACT FROM AUTHOR]

During sewage sludge incineration phosphorus (P) is retained in the ash in a form not directly available to plants. As P is a sparse resource, it is important to develop techniques for recovery of P from incinerated sewage sludge ashes (ISSA). Heavy metals are concentrated in ISSA and separation of P and heavy metals is required. The present work is an experimental screening of a new combination of acid extraction and electrodialysis–electrodialytic separation (EDS) for simultaneous P recovery and removal of heavy metals. Experiments were conducted with two different ashes; rich in Fe or Al. The separation method was best suited for the Fe-rich ash, where it was possible to separate P into one processing solution, heavy metals (Cu, Zn, Ni, Pb) into another, keeping the ash suspended in a third solution (which though still contained P after 1 week of EDS). For the Al rich ash, the separation was not similarly encouraging. The high release of Al during the extraction influenced the speciation of P and negatively charged P complexes were not prevailing. On the contrary to Al, the Fe containing ash particles were insoluble so Fe did not interfere with P speciation and separation after extraction. [ABSTRACT FROM AUTHOR]

Incineration is a traditional method of treating sewage sludge and the disposal of derived ash is a problem of secondary waste treatment. In this study, sewage sludge ash (SSA) was coated with ferrite through a ferrite process and then used as an adsorbent for ionic dyes (methylene blue [MB] and Procion Red MX-5B [PR]). The modified SSA possessed surface potential that provided electrostatic attraction toward MB and PR. Adsorbent FA10 (named on the basis of being produced from 10 g of SSA in the ferrite process) was used for the adsorption of MB. Ideal pH for adsorption was 9.0 and maximum adsorption capacity based on Langmuir isotherm equation was 22.03 mg/g. Adsorbent FA2.5 (named on the basis of being produced from 2.5 g of SSA in the ferrite process) was used for PR adsorption. Ideal pH for adsorption was 3.0 and the maximum adsorption capacity (calculated as above) was 28.82 mg/g. Kinetic results reveal that both MB and PR adsorption fit the pseudo-second-order kinetic model better than the pseudo-first-order model. The values of activation energy calculated from rate constants were 61.71 and 9.07 kJ/mol for MB and PR, respectively. [ABSTRACT FROM AUTHOR]

The nitrate removal rate of denitrifying granular sludge in an upflow sludge blanket reactor is very high and reaches up to 3.6 gNO3–N·gVSS−1 d−1at a nitrate loading rate (NLR) of 32.0 gNO3–N L−1 d−1. However, the granular sludge exhibits flotation under high NLR conditions, where the granules become large in size (of approximately 3–5 mm), light, and easily adhere to gas bubbles. In order to decrease the flotation potentiality of granular sludge, three measures were taken as follows: reducing the size of the granules, increasing the density of the granules, and weakening the adhesion effect of sludge to bubbles. While, these measures did not completely eliminate the granular sludge flotation. The way to solve sludge flotation namely instability was to slow down the biomass growth rate. The main factors to reduce denitrifying bacteria growth rate were verified as relatively low operating temperature, carbon source with comparatively slow degradation rate, and low NLR. Therefore, controlling denitrifying biomass growth rate via reducing temperature, replacing methanol with glucose as carbon source, and decreasing NLR was able to improve the stability of the granular sludge. [ABSTRACT FROM PUBLISHER]

Heavy metal removal from sewage sludge ash can be performed by mixing the ash with environmentally compatible chlorides (e.g. CaCl2 or MgCl2) and water, pelletizing the mixture and treating the pellets in a rotary reactor at about 1000 °C. Thermogravimetry–mass spectroscopy, muffle oven tests (500–1150 °C) and investigations in a laboratory-scale rotary reactor (950–1050 °C, residence time 1–25 min) were carried out. In the rotary reactor, up to 97% of Cu, 95% Pb and 95% Zn can be removed at 1050 °C. As Cl release starts from 400 °C (obtained from thermogravimetry–mass spectrometry experiments), heavy metals are already removed partially within the heating period. This heavy metal removal can be described as being similar to a first-order rate law. To meet the limit values specified in the Austrian and German fertilizer ordinances, residence times of the order of minutes are sufficient at 950 °C. [ABSTRACT FROM PUBLISHER]

Wastewater treatment by-products (WTBP), such as sewage sludge (SS) may be used to enhance soil chemical, physical, and biological properties. These enhanced soil properties, in turn, could from its source of production to its site of application. These concerns may be mitigated by incineration of the SS to produce ash (SSA) and dissolved in water and stored in ponds as contribute to an increase in plant growth, production, mineral nutrition. Some SS is difficult to handle due to bad odor in its raw state and has large mass, hence expensive for transportation weathered SSA (WSSA). A greenhouse study was conducted using Candler fine sand CFS; (CFS; pH = 6.8) and Ogeechee loamy sand OLS; (pH = 5.2) with application of either 0, 24.7, 49.4, 98.8, or 148.2 Mg ha−1 as either SS, SSA, or WSSA to evaluate the biomass production and elemental composition responses of sorghum-sudan grass (Sorghum vulgaris var. Sudanese hitche). Shoot and root biomass were 2 to 3 fold greater in the soil amended with SS, than either SSA or WSSA. Concentrations of nutrient and trace elements in the shoots and roots increased with increasing rates of amendments. Application of these by-products up to 98.8 Mg ha−1 rate did not adversely affect growth or accumulation of trace elements in sorghum-sudan grass. Long-term field studies are recommended to investigate the potential leaching of various elements from the amended soils in addition to evaluation of plant growth and production responses to determine the acceptable rates of these by-products as amendments to agricultural soils. [ABSTRACT FROM PUBLISHER]

Disposal of sewage sludge from waste water treatment plants is a serious environmental problem of increasing magnitude. Waste water treatment generates as much as 70 g of dry solids per capita per day. Although one of the disposal solutions for this waste is through incineration, still almost 30% of sludge solids remain as ash. This paper presents results related to reuse of sewage sludge ash in concrete. The sludge was characterised for chemical composition (X-ray flourescence analysis), crystalline phases (X-ray diffraction analysis) and pozzolanic activity. The effects of incineration on crystal phases of the dry sludge were investigated. Two water/cement (W/C) ratios (0.55 and 0.45) and three sludge ash percentages (5%, 10% and 20%) per cement mass were used as filler. The mechanical performance of sewage sludge ash concrete (SSAC) at different curing ages (3, 7, 28 and 90 days) was assessed by means of mechanical tests and capillary water absorption. Results show that sewage sludge ash leads to a reduction in density and mechanical strength and to an increase in capillary water absorption. Results also show that SSAC with 20% of sewage sludge ash and W/C = 0.45 has a 28 day compressive strength of almost 30 MPa. SSAC with a sludge ash contents of 5% and 10% has the same capillary water absorption coefficient as the control concrete; as for the concrete mixtures with 20% sludge ash content, the capillary water absorption is higher but in line with C20/25 strength class concretes performance. [ABSTRACT FROM PUBLISHER]

The degree of contamination with polycyclic aromatic hydrocarbons (PAHs) in soil samples in winter was determined. The contents of PAHs in samples were analyzed with HPLC. The PAHs contents of soil samples in winter around three different oily sludges from high to low represented the Third Wenming Plant of the oily sludge (3W), the Third Mazhai plant of the oily sludge (3M), and the Fourth Wener Plant of the oily sludge (4W), respectively. PAHs with 2-4 rings were major pollutants in oily sludge. Based on Nemero index P, the classification evaluation showed that soils around oily sludge were heavily polluted in winter. The health risk assessment and ecological risk assessment in soil in winter around oily sludge in Zhongyuan Oil Field was also analyzed. [ABSTRACT FROM AUTHOR]

In the present paper we show how P and NPK fertilizers can be prepared from thermochemically treated sewage sludge ashes (SSA) and which chemical reactions occur during these post-treatment steps. The SSA used for this investigation was treated thermochemically at a temperature of 1,000°C in a rotary kiln after the addition of calcium chloride hydrate or magnesium chloride hydrate to remove heavy metals and to increase the bioavailability of phosphorus (hereafter the products of thermochemical treatment are referred to as SSA-Ca and SSA-Mg). The major P-bearing mineral phase in SSA-Ca was chlorapatite (Ca5(PO4)3Cl), whereas in SSA-Mg the major P-bearing mineral phases were farringtonite (Mg3(PO4)2) and chlorapatite. Transformations of the mineral phases were observed when the P content of the products was adjusted by the addition of phosphoric acid (PA). The products of the reaction of SSA-Ca with PA were brushite (dicalcium phosphate dihydrate) and monocalcium phosphate monohydrate (MCPM). Further reaction products were found after the addition of PA to SSA-Mg: newberyite (MgHPO4·3H2O) and garyansellite ((Mg,Fe)3(PO4)2(OH)1.5·1.5H2O)). In addition, NPK fertilizers were prepared from SSA-Ca by mixing with molten NH4NO3 at approximately 180°C. No reaction occurred with the P-bearing mineral phase chlorapatite. When SSA-Ca was spiked with MCPM (to adjust the P content) before mixing it with molten NH4NO3, water-soluble NH4H2PO4 (monoammonium phosphate) was detected as a reaction product. [ABSTRACT FROM AUTHOR]

Sewage sludge ash can potentially be used for the removal of metal ions from wastewater because its chemical composition is similar to that of fly ash. The aim of this work was to investigate the adsorptive characteristics of this material, including specific surface area and pH of zero point of charge (pHzpc), and to assess the possibility of removing nickel and cadmium from aqueous solutions by this sorbent. The effects of agitation time, pH, initial metal ion concentration and temperature on the removal of these metals were studied. In order to study the sorption isotherm, two equilibrium models, the Langmuir and Freundlich isotherms, were analysed. The effect of solution pH on the adsorption on to sewage sludge ash was studied in the pH range from 2 to 8. The adsorption was endothermic and the computation of the parameters, ΔH°, ΔS° and ΔG°, indicated that the interactions were thermodynamically favourable. Experiments with Ni and Cd adsorption measured together showed that Cd severely interfered with Ni adsorption to sewage sludge ash and vice versa. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the synthesis of zeolites from paper sludge ash, and to evaluate their applications for water purification to simultaneously remove NH4+ and PO43- in aqueous solution. Paper sludge ash had a low abundance of Si and a significant Ca content, due to the presence of calcite that was used as paper filler. Na2SiO3 was added to the NaOH solution to increase Si content in order to synthesize zeolites with high cation exchange capacity. The original ash without addition of Si yielded hydroxysodalite with a cation exchange capacity of ca. 50 cmol/kg. Addition of Si to the solution yielded Na-P1 (zeolite-P) with a higher cation exchange capacity (ca. 120 cmol/kg). The observed concentrations of Si and Al in the solution during the reaction explain crystallizations of these two phases. The product with Na-P1 could simultaneously remove NH4+ and PO43- from the solution between pH 4 and 9. [ABSTRACT FROM AUTHOR]

A mathematical model (FPM) is presented to predict the transformation of heavy metals in the downstream of combustor or incinerator. The model accounts for the transformation of heavy metals through the combined effect of condensation,_nucleation, coagulation, external force and thermophoresis force. The calculation of heavy metals is embodied in the post-processor appended to Fluent soft. Before the simulation, velocity, temperature, PbCl2 concentration and other initial parameters are obtained by experiment. In addition, the transformation of PbCl2 is also experimentally studied. The comparison of experimental and predicted results indicate that the fine particle model (FPM) is valid for predicting the transformation of heavy metals in the downstream of incinerator or combustor. [ABSTRACT FROM AUTHOR]

The current study evaluated the effect of rotifers on the stability of aerobic granules. Two sequence batch reactors (SBRs) with airflow rates of 4 (R1) and 6 (R2) 1 min-1, respectively, were used to develop aerobic granules. Granules were well developed with excellent settleability in terms of SVI30 (sludge volume index,) of about 50 ml g-1 in both reactors at the beginning. With the outgrowth of rotifers, granules completely disintegrated in R1 around cycle 500 (a cycle was 3 hours). However, after the rotifers disappeared, i.e. cycle 550, granules re-appeared with a slow settling rate in R1 (SVI30: 200-300 ml g-1). The rotifers mechanically damaged the structure of granules, resulting in disintegration. However, granules developed under high shear force seem to have strong resistance to rotifers. During re-granulation, a long time lag between the improvements of morphology and settleability suggested that re-granulation resulted from entanglement more than bioattachment or bio-growth. Additionally, it was confirmed that the ratio of carbohydrate to protein extracellular polymeric substances (EPS) could well indicate the strength of granules. Protein EPS well correlated with the difference between SVI5 and SVI30 in R1, therefore, decreasing protein EPS would increase the compactness of granules. [ABSTRACT FROM AUTHOR]

A new activated sludge process modification was proposed for intermittent aeration process to achieve more stable nitrogen removal performance. A single completely mixed reactor was divided into two compartments in series and operated in intermittent aeration mode by using activated sludge simulation model. The new configuration provided competetive advantage on nitrification as well as denitrification capacity, compared to the intermittently aerated system with a single reactor. In addition, the dissolved oxygen set-point control during air-on periods was found to be an important parameter in terms of nitrogen removal. [ABSTRACT FROM AUTHOR]

Oil shale processing produces an aqueous wastewater stream known as retort water. The fate of the organic content of retort water from the Stuart oil shale project (Gladstone, Queensland) is examined in a proposed packed bed treatment system consisting of a 1:1 mixture of residual shale from the retorting process and mining overburden. The retort water had a neutral pH and an average unfiltered TOC of 2,900 mg l-1. The inorganic composition of the retort water was dominated by NH4+. Only 40% of the total organic carbon (TOC) in the retort water was identifiable, and this was dominated by carboxylic acids. In addition to monitoring influent and effluent TOC concentrations, CO2 evolution was monitored on line by continuous measurements of headspace concentrations and air flow rates. The column was run for 64 days before it blocked and was dismantled for analysis. Over 98% of the TOC was removed from the retort water. Respirometry measurements were confounded by CO2 production from inorganic sources. Based on predictions with the chemical equilibrium package PHREEQE, approximately 15% of the total CO2 production arose from the reaction of NH4+ with carbonates. The balance of the CO2 production accounted for at least 80% of the carbon removed from the retort water. Direct measurements of solid organic carbon showed that approximately 20% of the influent carbon was held-up in the top 20cm of the column. Less than 20% of this held-up carbon was present as either biomass or as adsorbed species. Therefore, the column was ultimately blocked by either extracellular polymeric substances or by a sludge that had precipitated out of the retort water. [ABSTRACT FROM AUTHOR]

Several batch studies that were made up of the acid extraction and the solvent extraction were performed to recover phosphorus from the waste-activated sludge (WAS) incinerator ash. In the acid extraction, the extraction efficiency of phosphorus relied on the acid type, liquid(acid)-to-solid (LacidS) ratio, and acid concentration. Phosphorus in the WAS incinerator ash was completely extracted by 1 M HCl at the LacidS ratio of 6.4:1. Subsequently, the solvent extraction was conducted to separate and concentrate phosphorus further from the acid extract. The efficiency of solvent extraction was affected mainly by the solvent type, liquid (solvent)-to-liquid (the acid extract) (LsolvLacid txt) ratio, and hydrogen ion concentration. Under the appropriate condition, 76% of phosphorus in the acid extract was extracted to 1-butanol phase, which corresponded to 80.1% as the mass fraction of phosphorus to total elements. Prior to the solvent extraction, the addition of bis (2-ethylhexyl) phosphoric acid (D2EHPA), which was available for removing aluminum from the acid extract, led to an additional increase in the term of the mass fraction of phosphorus to total elements. Overall results indicated that phosphorus in the WAS incinerator ash could be efficiently recovered and be a potential renewable resource. [ABSTRACT FROM AUTHOR]

This work presents conditions for hexavalent chromium (Cr(VI)) removal from aqueous solution using different sorbent materials, namely: pyrolytic ashes of an industrial sludge from wastewater treatment and roots of Typha latifolia. The sorbent materials were characterized using scanning electron microscopy (SEM) and surface area using theBrunauer-Emmett-Teller (BET) technique, before and after the contact with the chromium-containing aqueous media. An overall Cr(VI) concentration reduction of 45 % was achieved using the roots of Typha latifolia whereas in the case of pyrolytic ashes a 60 % removal was observed. The percentage removal was found to depend on the initial Cr(VI) concentration in aqueous solution, pH and temperature. The Cr(VI) uptake process was maximum at pH 2 and a temperature of 40 °C for both sorbents. These materials showed a Cr(VI) adsorption capacity that was adequately described by the Langmuir adsorption isotherm. It was demonstrated that the use of waste materials for the treatment of Cr(VI)-containing wastewater is an effective and economical alternative method. [ABSTRACT FROM AUTHOR]