Water Treatment Sludge Research Articles

Phosphorus Adsorption in Water and Immobilization in Sediments by Lanthanum-modified Water Treatment Sludge Hydrochar

Using water treatment sludge and lanthanum chloride as raw materials, lanthanum-modified water treatment sludge hydrothermal carbon was prepared through one-step hydrothermal carbonization and loading lanthanum. SEM-EDS, BET, FTIR, XRD, and XPS were used to characterize the materials. The initial pH of the solution, adsorption time, adsorption isotherm, and adsorption kinetics were investigated to study the adsorption characteristics of phosphorus in water. The results showed that the specific surface area, the pore volume, and the pore size of the prepared materials were significantly increased, and the phosphorus adsorption capacity was greatly improved compared with that of the water treatment sludge. The adsorption process conformed to the pseudo-second-order kinetic model, and the Langmuir model fitted the maximum phosphorus adsorption capacity to 72.69 mg·g-1. The main adsorption mechanisms were electrostatic attraction and ligand exchange. Adding lanthanum-modified water treatment sludge hydrochar into the sediment could effectively control the release of endogenous phosphorus from the sediment to the overlying water. According to the analysis of phosphorus forms in sediment, the addition of hydrochar promoted the transformation of unstable NH4Cl-P, BD-P and Org-P into the very stable HCl-P in the sediment, which reduced the content of potential active phosphorus and also significantly reduced the content of biologically available phosphorus. This indicated that lanthanum-modified water treatment sludge hydrochar could effectively adsorb and remove phosphorus in water and could also be used as sediment improvement material to effectively stabilize endogenous phosphorus in sediment and control phosphorus content in water.

Comparative study of sediment phosphorus immobilization via the addition of lanthanum-modified and thermal-modified drinking water treatment sludge.

Lanthanum-modified drinking water treatment sludge (DTSLa) and thermal-modified drinking water treatment sludge (TDTS) were prepared from drinking water treatment sludge(DTS). The adsorption properties of DTSLa and TDTS on phosphate in water and the effects on the controlled release and morphology of phosphorus in sediment at different dosages (0%, 2.5%, 5%) were discussed. Combining with SEM, BET, XRD, FTIR, and XPS characterization methods, the immobilization mechanism of DTSLa and TDTS on phosphorus in sediment was explored. The addition of TDTS can transform NH4Cl-P (loosely sorbed P), BD-P (bicarbonate-dithionite extractable P), and Org-P (organic P) into stable NaOH-rP (metal oxide-bound P) in sediment, and the conversion amount will increase with the increase of TDTS supplemental amount. DTSLa converted NH4Cl-P, BD-P, Org-P, and NaOH-rP to more stable HCl-P (calcium-bound P). At the same time, the content of WSP (water-soluble phosphorus) and olsen-P (NaHCO3 extractable P) in sediment can be reduced by the addition of DTSLa and TDTS, reducing the risk of the release of phosphorus from the sediment to the overlying water. In addition, phosphorus can be directly removed from the interstitial water by DTSLa and TDTS, so as to reduce the phosphorus concentration gradient between the overlying water and the interstitial water, thus inhibiting the release of phosphorus from interstitial water to overlying water. The results showed that DTSLa is better than TDTS in terms of its adsorption capacity and adsorption effect on endogenous phosphorus in water, so DTSLa is more suitable to be used as a sediment conditioner to control the phosphorus content in water and sediment.

Ecological Footprint Assessment of Concrete: Partial Replacement of Cement by Water Treatment Sludge and Stone Dust

Currently, most concrete industries use conventional cement (Ordinary Portland Cement) as a binding material which involves natural resource depletion, colossal CO2 emissions, and a huge energy supply. The present study addresses this critical issue by using stone dust (sun-dried and calcinated) and water treatment sludge (sun-dried and calcinated) to replace cement partly in M20-grade concrete production. The environmental impact of ready-mixed concrete (RMC) production with conventional cement and partially replaced cement by other cementitious material, i.e., stone dust and water treatment sludge in concrete, is assessed through ecological footprint (EF) indicator. Moreover, a novel sustainability index is proposed for ready-mixed concrete plants to scale the environmental impact of different types of concrete (or grades) on the sustainability scale (environmental, social, and economic sustainability). The results showed that the sun-dried water treatment sludge and sun-dried stone dust could effectively replace cement (15% by weight) in the concrete, with a comparable compressive strength over the M20 ready-mixed concrete. The EF of conventional M20 RMC is estimated to be 0.02295 gha/m3. The EF of concrete (with sun-dried water treatment sludge) is reduced by 13.14% of the conventional ready-mixed concrete. The Ecological Sustainability Index (ESI) of the ready-mixed concrete plant is estimated to be 718.42 $/gha. Using water treatment sludge and stone dust in concrete production can be an innovative solution because it simultaneously solves the problem of waste disposal, large carbon emissions, cost, and high environmental impact.

Life Cycle Assessment of a system for the extraction and transformation of Waste Water Treatment Sludge (WWTS)-derived lipids into biodiesel

In recent years, the demand for biofuels has been growing exponentially, as has the interest in biodiesel produced from organic matrices. Particularly interesting, due to its economic and environmental advantages, is the use of the lipids present in sewage sludge as a raw material for the synthesis of biodiesel. The possible processes of this biodiesel synthesis, starting from lipid matter, are represented by the conventional process with sulfuric acid, by the process with aluminium chloride hexahydrate and by processes that use solid catalysts such as those consisting of mixed metal oxides, functionalized halloysites, mesoporous perovskite and functionalized silicas. In literature there are numerous Life Cycle Assessment (LCA) studies concerning biodiesel production systems, but not many studies consider processes that start from sewage sludge and that use solid catalysts. In addition, no LCA studies were reported on solid acid catalysts nor on those based on mixed metal oxides which present some precious advantages, over the homogeneous analogous ones, such as higher recyclability, prevention of foams and corrosion phenomena, and an easier separation and purification of biodiesel product. This research work reports the results of a comparative LCA study applied to a system that uses a solvent free pilot plant for the extraction and transformation of lipids from sewage sludge via seven different scenarios that differ in the type of catalyst used. The biodiesel synthesis scenario using aluminium chloride hexahydrate as catalyst has the best environmental profile. Biodiesel synthesis scenarios using solid catalysts are worse due to higher methanol consumption which requires higher electricity consumption. The worst scenario is the one using functionalized halloysites. Further future developments of the research require the passage from the pilot scale to the industrial scale in order to obtain environmental results to be used for a more reliable comparison with the literature data.

Oxygen carrier derived from ferric sludge for chemical looping combustion of MSW syngas: Waste derived material performance and carbon footprint assessment

The utilization of water treatment sludge (i.e., ferric sludge) was explored as the oxygen carrier (OC) for chemical looping combustion (CLC) of municipal solid waste (MSW) syngas. The performance of ferric sludge (FS) in CLC and simultaneous HCl removal was evaluated in a bench-scale fluidized bed, and was compared with iron ore (IO) as a benchmarked OC. The results show that FS (92 %) performed better than IO (82 %) in terms of syngas combustion efficiency and FS was able to remove HCl (77 % removal efficiency) while IO was unable to remove any HCl. Comparison of reaction temperature reveals that FS performed better at lower CLC temperature between 800 °C and 850 °C. Agglomeration was observed when FS was used in extended CLC cycles. Thus, investigation of using inert α-Al2O3 support together with FS for extended CLC cycles was investigated. Agglomeration and sintering were drastically reduced and good combustion efficiency of 88 % for H2 and 74 % for CO was attained. Carbon footprint assessment illustrated that FS was superior as a greener material based on global warming potential of 20 and 100 years. Conversion of FS as an OC were characterized with 104.23 and 108.0 kgCO2/t lower than IO for GWP-20 and GWP-100, exhibiting the competitiveness in the usage of waste-derived material in CLC. Hence, FS can be considered as a novel, cost-effective, and greener OC for CLC. The co-utilization of waste-derived material and waste-derived syngas through CLC would be an integrated solution for improved circularity and sustainability.

Partitioning and transformation behavior of Cd(II) and As(V) during As(V)-Cd(II)-Fe(III) coprecipitation: Effect of aging under aerobic conditions at pH 5 and 11 relevant to tailings and acid waste

Aerobic coprecipitation and subsequent aging of the As(V)-Cd(II)-Fe(III) system are ubiquitous processes in engineered settings, natural shallow water, surficial soils, and mine tailings. Herein, we have investigated the partitioning of As(V) and Cd(II) coupled with the solid evolution during As(V)-Cd(II)-Fe(III) coprecipitation and subsequent aging process under aerobic conditions at different pH (5 and 11) and Fe(III)/As(V) ratios (10 and 40) with various Cd(II) concentrations at 90 °C. X-ray diffraction and transmission electron microscopy results reveal that ferrihydrite is the dominant phase in the initial coprecipitates, regardless of pH and the coexisting As(V) and Cd(II). Low pH and high Fe(III)/As(V) ratios favor the transformation of initial ferrihydrite to hematite during the aging process, which can further promote the incorporation of ferrihydrite-bound As(V) and Cd(II) into stable hematite. Chemical analyses indicate that the partitioning fractions of adsorbed/extractable and solid-incorporated As(V) and Cd(II) are controlled by pH, Fe(III)/As(V) ratio, and aging time during ferrihydrite transformation. High Fe(III)/As(V) ratios facilitate the incorporation of the extractable Cd(II) into the aging intermediates, whereas the As(V) partitioning is less affected by the initial Cd(II) concentration. The crystallization rates of ferrihydrite at high Fe(III)/As(V) ratios or low pH are higher than those at low Fe(III)/As(V) ratios or high pH. Furthermore, increased Cd(II) concentrations significantly reduce the crystallization rates of the initial ferrihydrite. These findings have shed new light on the mobility and transformation behavior of toxic As(V) and Cd(II) in the As(V)-Cd(II)-Fe(III) coexisting environment under aerobic conditions and are useful for developing novel As(V)-Cd(II)-compound contaminant management strategies for metallurgical waste residues and water treatment sludges.

Investigation of water treatment sludge for the treatment of saline water: Batch studies

In this study, water treatment sludge was investigated through batch modes for the treatment of saline water to meet livestock drinking consents. The water quality was assessed using water quality index (WQI).The kinetic data was best described by the Pseudo – Second – Order model and the equilibrium isotherm by the Freundlich model. The maximum removal efficiency was 51.5 ± 0.65%, 22.6 ± 0.5% and 100% for Sulphates (SO42−), Chloride (Cl−), and Nitrates (NO3−), respectively. The maximum removal efficiency of sodium (Na) and nickel (Ni) was 100% each at 0.4g dose and that of manganese (Mn) was 87.5% at 1.2g dose. The effect of temperature revealed that the adsorption capacity for anions, decreased with increasing temperature, whereas for the cations the adsorption capacities increased with increasing temperature. The water treatment sludge reduced the total dissolved solids (TDS) and electrical conductivity (EC) from the initial values of 19600 mgL−1 and 38900 μScm−1 to 98 mgL−1 and 1728 μScm−1,respectively. The Water Quality Indices were 37.35 and 7.57, before and after treatment, respectively. Water treatment sludge can be used for the pre-treatment process before using conventional treatment technologies. Pilot scale investigations should be conducted before field trials.

Investigation on the suitability of aluminium-based water treatment sludge as a sustainable soil replacement for road construction

Water treatment sludge is a by-product of the drinking water treatment process, and it has been considered as a waste for water authorities around the world. This study aims to investigate the reuse of aluminium-based water treatment sludge (AS) as a soil replacement in road construction which can improve sustainable waste management practices for positive environmental outcomes. To evaluate the potential reuse of AS, a 50/50 mixture ratio of AS and clay (CL) was selected and tested for geotechnical engineering parameters through Odometer Tests, Unconfined Compression Strength Tests, Static triaxial, Cyclic triaxial and California Bearing Ratio. Detailed physical and chemical were also conducted with the water treatment sludge. Results suggest that combining AS with CL increases the optimal moisture content and decreases the dry density of the soil. Oedometer tests indicated that the CLAS mixture distributed stress better than CL and AS independently. In the UCS tests, CLAS enhanced the strength of the mixture from 74 kPa with only CL to 126 kPa with the introduction of AS. The shear strength of CLAS samples increased by 50% compared to CL. In the cyclic triaxial test, CLAS showed less cumulative strain than CL, and improved the CBR results of the mixture from 0.95% to 1.92%. Results indicate that AS can be beneficially reused as a low-cost soil replacement to contribute the Circular Economy and net-zero emission targets. Future research should examine the variability of AS, optimal ratios of AS to CL, and the levelized cost of AS in different environmental conditions.

Utilization of manganese-rich sludge in concrete: Mechanical, nanoscale characteristics and leaching behavior

The management and recycling of heavy metal-rich sludge have posed serious environmental challenges. High levels of potassium permanganate are often used to treat eutrophic water bodies, which produce manganese-rich drinking water treatment sludge (DWTS). Although there have been some studies on recycling sludge in cement-based materials, little attention has been paid to the multiscale behavior of concrete with manganese-rich sludge. In this study, eco-friendly concrete was produced by substituting part of the cement with calcined DWTS (CWTS), and its mechanical properties, drying shrinkage, microstructure, and environmental characteristics were systematically investigated. The results showed that the incorporation of an appropriate amount of CWTS improved the mechanical properties and volume stability of the concrete, and the best performance was achieved when the substitution level was 10%. The 90-d compressive strength of 10% CWTS-modified concrete was relatively increased by 7.91%, while the 150-d drying shrinkage was relatively reduced by 14.84% compared with plain concrete. The pozzolanic action of CWTS consumed part of Ca(OH)2 and increased the degree of reactivity of the paste at appropriate substitution levels. From the perspective of nanoscale characteristics, the incorporation of 10% CWTS reduced the content of the pore phase and clinker and increased the content of the C-S-H phase relative to plain concrete, where high-density C-S-H and low-density C-S-H increased by 12.5% and 6.8%, respectively. Moreover, incorporating an appropriate amount of CWTS also reduced the width of the interfacial transition zone (ITZ), but with the further increase of its content, the width of the ITZ increased. In addition, CWTS-modified concrete not only exhibited safe heavy metal leaching behavior but also had lower costs and carbon emissions. This study provides new insights into the management and recycling of DWTS, especially manganese-rich sludge obtained from the treatment of algal blooms.

Characterization and utilization of water treatment sludge for coagulation of raw water.

One of the critical steps in the treatment of raw water for human consumption is clarification. It encompasses coagulation and flocculation to reduce the concentration of suspended solids in turn producing a semi-solid slurry called water treatment sludge (WTS). It is necessary to characterize and find economic and sustainable ways to utilize the WTS. The WTS used in this work was characterized and contained aluminum (Al) (20.3% Al2O3) and iron (Fe) (5.28% Fe2O3) making it suitable for the development of a coagulant. A less energy-intensive way, through atmospheric acid leaching of WTS, was developed to extract Al and Fe for use as a coagulant. The sulphuric acid concentration and solid loading that gave the highest Al concentration were determined to be 3N and 5 g/100 mL, respectively. Turbidity reduction achieved with the developed coagulant ranged from 91 to 99% and was higher than that obtained in related studies due to the higher concentrations of Al and Fe in the WTS used in this study. Since the coagulant was very acidic, it was co-dosed with calcium oxide at 10 g/L of water to adjust the pH of the final water to allowable pH values for potable water (6.5-9.5).

Using water treatment sludge to Improve Geotechnical Engineering Properties of Soils: A Review

Water treatment sludge (WTS) is a byproduct generated during the treatment of wastewater. In recent years, researchers have explored the potential of using WTS as a soil stabilizer to improve the geotechnical properties of soils. In this review, we will examine the current state of knowledge on the use of WTS for this purpose. The organic matter content of WTS is usually high and can range from 30% to 60%. The high organic matter content makes WTS a potential source of nutrients for plants, and it can also enhance soil structure and water retention. Another important consideration is the environmental impact of using WTS. The use of WTS can be an eco-friendly alternative to chemical stabilizers, which can have adverse effects on the environment. However, there are concerns about the potential for heavy metal contamination in WTS. To mitigate this risk, it is recommended to conduct thorough testing of WTS before using it as a soil stabilizer. Finally, the use of WTS as a soil stabilizer has the potential to improve the geotechnical properties of soils. However, it is essential to consider factors such as the type and dosage of WTS, the soil type, and the environmental impact before using it. Further research is also needed to explore the potential of using WTS in different soil types and environmental conditions.

Mesocosm Evaluation of the Safety of the Use of Reclaimed Water Regarding Emerging Pollutants in Murcia, Spain

The increasing shortage of conventional water for crop irrigation in arid and semiarid regions is encouraging the use of nonconventional water resources. Nevertheless, concern about the presence and possible negative effects of emerging contaminants in reclaimed water can cause individuals to avoid using these water sources. To clarify the guarantees that reclaimed water offers, a mesocosm study was carried out. Lettuce plants were cultivated in pots watered with three different types of water (distilled, reclaimed, and spiked with contaminants of emerging concern). The results showed low concentrations of contaminants in the leachates and plant tissues when the reclaimed water was used. However, their concentrations were high when the pots were watered with the spiked water; this was mainly true for carbamazepine, which reached a maximum of 2982 ng L−1 in the leachates and 45.2 ng g−1 in the plant roots. In the lettuce watered with the spiked water, carbamazepine was found in the edible part at very low concentrations that did not imply any human risk. Finally, an acute toxicity test was performed on the leachates, which were found to be only slightly toxic in the spiked water. This work indicates that with the current technical improvements in active sludge water treatment, reclaimed water can be used for irrigation without the risk of contamination by contaminants of emerging concern.

Turbidity Reduction and Eco-friendly Sludge Disposal in Water Treatment Plants

Plankton and other microscopic colloids are tiny particles that are suspended in water and cause turbidity, which causes the water to seem murky or opaque. These particles are too unstable and light to settle or be naturally eliminated. These details contribute to water turbidity and pose some stability. During the process of purifying raw water, all water treatment Plants (WTPs) produce waste/residue known as water treatment sludge (WTS). The majority of the sludge’s chemical components include silica, alumina, ferric oxide, lime, and many heavy metals. The surface water treatment technique included coagulation, flocculation, sedimentation, and filtration to remove colloidal and suspended particles from raw water. The sludge obtained from the WTP located at Kekri (Rajasthan), India is being investigated for its physical and chemical properties. About 60% of the sand contained in the sludge is found in the 155-60 grain size range. Additionally, nutrient reduction of soil due to contamination and runoff can be minimized or rounded out by wastewater treatment or the removal of heavy metals from water solutions. To develop water-safe and appealing sludge management solutions, the efficiency of aluminum sulfate and poly aluminum chloride was assessed at different coagulant doses in the study. To make water safe and appealing for human consumption, numerous purification procedures are employed from a variety of sources. Sludge bricks are acceptable to high temperatures in the furnace and have better compressive strength than clay bricks.

Characterizing and processing a kaolinite-rich water treatment sludge for use as high-reactivity pozzolan in cement manufacturing

This paper evaluates the potential of water treatment sludge ash (WTSA) as high-reactivity pozzolan using strength tests in mortars and techniques to evaluate the calcium hydroxide consumption in pastes with hydrated lime. The sample was dried in an oven and then calcined at 600, 700, and 800 °C in a muffle. A high-reactivity metakaolin sample was used as a pozzolan reference. The properties of the samples assessed were fineness (Blaine), density (Le Chatelier), and chemical and mineralogical composition using X-ray diffraction (XRD), X-ray fluorescence (XRF), and thermogravimetric analysis (TG). The assessment of the pozzolanic properties employed standardized tests such as compression tests with hydrated lime (NBR 5751) and Portland cement (NBR 5752) in mortars. Also, non-standardized techniques, such as XRD, TG, and electrical conductivity, were utilized to evaluate the consumption of calcium hydroxide in pastes and solutions with hydrated lime and pozzolan. The standardized tests showed that mortars with metakaolin (MK) presented higher compressive strength values, while mortars with ash calcined at 600 °C (SA600) obtained the lowest values among WTSA. This behavior occurred because the preparation of mortars was strongly influenced by their consistency, affecting the compressive strength. However, analyzing the consumption of calcium hydroxide in pozzolan-hydrated lime pastes, SA600 presented higher values. Unlike tests on mortars, consistency is not affected in preparing the pastes, allowing a better development of pozzolanic reactions. Based on Ca(OH)2 consumption, it was concluded that the samples of WTSA studied could be used as high-reactivity pozzolans.

Recycling of water treatment sludge in concrete: The role of water-binder ratio from a nanoscale perspective

For eutrophic water bodies, potassium permanganate is an effective pre-oxidant to remove algae and its residue in water treatment sludge. Recycling water treatment sludge in concrete is an environmentally friendly and high-value utilization measure. However, little research has been done on the effect of manganese-rich drinking water sludge ash (DWSA) on concrete. The effect of water-binder ratio (w/b) on strength, shrinkage and microstructural characteristics of concrete containing DWSA was investigated, and the structural behavior was explained from a nanoscale perspective. The results show that recycling 10 % DWSA in concrete improved the strength and shrinkage resistance of the samples. Reducing the w/b effectively increased the strength of DWSA-modified concrete and reduced the shrinkage deformation. The paste with high w/b had higher contents of non-evaporated water and calcium hydroxide, as well as higher reaction degree of DWSA. Nanoscale characterization shows that reducing the w/b reduced the volume fraction of pore and unhydrated phases in the matrix and increased the proportion of high-density C-S-H. Meanwhile, reducing the w/b also reduced the interfacial transition zone width of DWSA-modified concrete. Recycling DWSA in concrete effectively reduced the total carbon footprint and cost of the mixture. The combined application of reducing the w/b and incorporating DWSA effectively improved the economic and environmental benefits of concrete material. For the concrete modified with 10 % DWSA (w/b = 0.3), its cost and carbon emissions are reduced by 14 %–21 % and 19 %–25 % compared with the reference sample, respectively. Overall, this study reveals the action mechanism of DWSA in cement system at different w/b from nanoscale perspective, and gives a new insight on determining the optimal w/b in full-scale application of DWSA concrete.

Rheological Behavior and Characterization of Drinking Water Treatment Sludge from Morocco

Drinking water treatment generates a high amount of pasty by-product known as drinking water treatment sludge (DWTS). The chemical composition, microstructure and rheological behavior of DWTS are of utmost importance in the calculation, design, optimization, commissioning and control of its treatment processes. The purpose of this research was to characterize the DWTS from the drinking water treatment plant of Marrakech (Morocco), aiming to help future researchers and engineers in predicting its hydrodynamic behavior. The first part of this study was devoted to the physical structure and the chemical composition of sludge. The second part was oriented towards the study of the mechanical properties; a penetration test and a rotational rheology test were performed. For the first test, a force–length penetration diagram was plotted in order to calculate the hardness, the cohesiveness and the adhesiveness of DWTS. For the second test, the shear stress and the apparent viscosity were plotted and fitted to five rheological models, as function of the shear rate, aiming to describe the rheological behavior of samples. The obtained results reveal that the drinking water treatment sludge from Marrakech is a porous, amorphous and highly adhesive material, with a shear-thinning (pseudoplastic) rheological behavior that can be described according to the Herschel–Bulkley model (better in low-rate stresses, R² = 0.98) or the Windhad model (better in high shear rates, R² = 0.96) and is mainly composed of silica, aluminum and iron oxides.

Fabrication of porous mullite‐based ceramic bricks from Al‐rich water treatment sludge and kaolinitic‐based clay

Fabrication of porous mullite‐based ceramic bricks from Al‐rich water treatment sludge and kaolinitic‐based clay

Evaluation of Reinforcement Corrosion in Cementitious Composites Modified with Water Treatment Sludge

The water treatment sludge (WTS) is a residue composed of organic and inorganic matter in a solid, liquid, and gaseous state that has a variable composition concerning its physical, chemical, and biological characteristics. The irregular disposal of WTS can promote harmful changes to the environment, such as reduction of dissolved oxygen and increase in the concentration of aluminum and other metals in the receiving watercourses. To propose a suitable purpose for this residue, this work evaluated the physical and mechanical properties of the concrete and corrosion resistance of the reinforcement in a cementitious composite using WTS in replacement to the natural sand. A conventional concrete and a conventional mortar were used as a reference and a 3% WTS-content concrete, and a 3% WTS-content mortar were prepared to evaluate the WTS influence in mechanical properties and corrosion resistance. By electrochemical measurements, it was observed that the resistance of the cementitious matrix was not altered by WTS addition. Regarding steel resistance, the WTS may promote a higher susceptibility to frame corrosion, which can be correlated to the lower pH than reference medium (REF). The concrete reinforcement characterization indicates that concretes with WTS can be used as reinforced concrete structure in urban areas.

Using a Laboratory Model Test to Evaluate Collapsibility of Gypseous Soils Improved by Sludge

Collapsibility of gypseous soils may cause excessive settlement and severe damage to engineering structures. Many improvement methods have been employed to reduce the collapsibility of these soils, such as by using physical methods or chemical additives. The collapsibility of the improved gypseous soils has conventionally been evaluated by using the odometer test, which may not accurately replicate the field conditions because of the small size of the test specimens. In this research, a laboratory model test of 600x600x600 mm with a model footing of 100x100mm was developed to measure the collapse characteristics of sandy soil with a gypsum content of 37%. The test was first conducted on specimens in the model at three different relative densities. The test was then performed after compacting the top layer of the test specimens [thickness from 50 to 100 mm] to the maximum dry density, as obtained from the Standard Compaction Test. Water treatment sludge was also used to further improve the top compacted layer. The results indicated that the collapsibility settlement reduction factor was 75% when the top layer of 50 mm thickness was compacted to the maximum dry density. Additionally, when the sludge was used with the top layer, the collapsibility settlement reduction factor was 86%.

Potential of silica from water treatment sludge modified with chitosan for Pb(II) and color adsorption in sasirangan waste solution

Water treatment sludge (WTS) still contains a lot of silica oxide (SiO2) as much as 43.12-66.90% by weight and can act as an adsorbent to be applied to the treatment of Sasirangan wastewater. Silica extraction from WTS was carried out by microwave-assisted leaching, which - compared to conventional extraction - had several advantages including high extraction yields, fast, uniform, and more selective processing time. In addition, Sasirangan liquid waste is a by-product of the dyeing process of Sasirangan cloth, which still contains heavy metals in amounts exceeding the quality standard. This study aims to extract silica from WTS by microwave-assisted leaching process to synthesize silica modified by chitosan (Si-Kit) as an adsorbent to reduce Pb(II) from Sasirangan wastewater, and to obtain a kinetic model of the adsorption process. The silica from microwave-assisted leaching process (Si-MaL) and Si-Kit adsorbents were characterized using FTIR and SEM. The results showed that the dominant functional groups of Si-Kit included Si-O-Si, Si-O-C stretching vibrations, and stretching vibration of C=N showing that the condensation between aldehyde groups and amino groups occurred to form base after the addition of glutaraldehyde. The SEM images showed that Si-MaL and Si-Kit adsorbent obviously increased in particle size with the presence of visible particles of homogeneous granules and large pores. The removal efficiency percentage of Pb(II) and color occurred at 6% w/v adsorbent weight and 70 min was 87.20% and 61.87% respectively. Meanwhile, the adsorption kinetics of Pb(II) and color followed the zero order kinetics model at weight variation of 6%-w/v based on the value of R2 close to one and the adsorption capacity of Pb(II) ion and color were 12.01 mg g-1 and 467 mg g-1, respectively.