Recycling Of Sludge Research Articles

Sequential 'acid leaching-anion exchange-aerobic composting' process for recycle of municipal sludge.

Municipal sludge disposal and recycle has become a prominent research theme. In this study, a sequential process for integral treatment of municipal sludge was primarily presented, combining acid leaching, anion exchange and aerobic composting. The aim of the process was to remove chromium (Cr) from the sludge and reuse the sludge as manure. Firstly, Cr was removed from municipal sludge via the acid leaching process; the removal rate was up to 57.43%. Then, ion exchange resin was used to remove Cr from leachate; the removal rate reached 95%. Aluminum sheet was used to replace the Cr from eluent; the replacement rate was 63.3%. The aerobic composting process could be successfully warmed up to above 55 °C and lasted for 4 days; the seed germination index reached 68.3%. After the composting process, the residual Cr in sludge mainly existed at a more stable residual state and organic binding state. Overall, this novel sequential process serves as a potential high-efficiency, green, low-energy way for municipal sludge recycle.

Recycling of High-Purity Strontianite and Hematite from Strontium-Bearing Sludge.

Sr-bearing sludge is a hazardous waste that is commonly generated by nuclear power plants and mineral refining operations. In this work, Sr-bearing sludge was simulated and then cleanly recycled into high-purity strontianite with hematite nanoparticles as a byproduct via a novel hematite precipitation route. The sludge contained 26.1% Fe, 3.5% Sr, and Si impurities. After dissolution in 1.2 M nitric acid, the sludge was treated hydrothermally with the addition of glycol to precipitate Fe effectively. Without the addition of glycol, only 52% Fe was hydrothermally precipitated in the form of hematite aggregates. With the addition of glycol at the optimal Mglycol/Mnitrate molar ratio of 0.4, nearly 100% Fe was removed in the form of hematite nanoparticles with an average diameter of 50 nm, whereas over 98% of Sr was retained in the leachate. The generated hematite was highly purified with an Fe2O3 content of 95.23%. Sr was present at a high concentration of 3.9 g/L in the treated leachate and further precipitated in the form of strontianite with a purity of 96.8% through Na2CO3 addition. Tertiary butanol (TeB) exhibited a similar Fe removal rate as glycol even though its optimal MTeB/Mnitrate molar ratio was 0.1, which was approximately one-fourth the optimal Mglycol/Mnitrate molar ratio. Fe removal involved spontaneous Fe3+ hydrolysis under hydrothermal conditions and was promoted by increasing the pH of the redox reaction between nitrate and glycol and/or TeB. The method reported here successfully enabled the resource recycling of Sr-bearing sludge to generate high-purity strontianite and hematite products without producing any secondary waste.

Recycling of raw water treatment sludge in cementitious composites: effects on heat evolution, compressive strength and microstructure

Water treatment sludge (WTS) is produced daily and represents a globally significant solid waste stream. The application of this sludge as construction materials has been studied although most studies have modified the sludge before its incorporation, hence involving significant energy consumption. This study aims to use raw sludge as a novel cementitious material, by determining the effects of sludge addition on the composition and performance of cementitious composites. Important aspects such as the physicochemical interaction of the raw sludge with the Portland cement, the heat evolution of the cement paste and the compressive strength of the composite cement were carefully studied. The results show that for 1-2% of WTS addition, the compressive strength and heat evolution of the cement paste was well maintained being close to the reference specimen after 28 days of curing. However, for sludge addition above 5%, a delay in the hydration reaction was observed, together with about 25% reduction in compressive strength at 28 days of curing. The mineralogical and thermal analysis showed decreasing portlandite content and increasing calcite in the WTS-amended composites. Scanning electron microscope analysis demonstrated that the addition of sludge induced more porous and weak surface structures compared to the reference specimen.

HEAVY METAL ACCUMULATION IN DIFFERENT PARTS OF TREES GROWN ON SEWAGE SLUDGE

Sewage sludge is a rest product deriving from the wastewater treatment plants. It is rich in nutrients and essential elements. Therefore sludge on-land utilisation can create an added value by recovering energy from biomass produced on marginal lands. However, widespread on-land recycling of sewage sludge might be limited due to high heavy metal content. Health organisations show an increasing concern about the risks posed to the environment and human health as many countries worldwide already are facing the heavy metal contamination problem. In the scientific literature it can be found, that high total heavy metal content is not directly related to an intensive metal uptake by plants. In this study samples were collected from three woody plant species (black locust, silver birch and aspen) growing directly on the sewage sludge in a storage site near Kaunas, Lithuania. Heavy metal content was detected separately in the leaves, stems and roots. It was determined that nearly all analysed heavy metals (lead, chromium, nickel, copper and zinc) were accumulated within normal range despite high total concentrations in the growing media, and only cadmium was accumulated at elevated concentration. Based on bioaccumulation factor, aspen could be considered as a Cd-accumulator and used for phytoremediation purposes.

Current Status of Technology and Standards of Sludge Recycling in China

This paper sorts and analyzes current states of technologies and standards, existing problems and demands of the sludge recycling industry in China, in order to further promote the establishment of sludge recycling standard system in China, standardize key technologies, devices and processes of efficient sludge recycling, and promote the application and utilization of advanced technical equipment, thus providing solid technical support and guarantee for the enhancement of overall performance level and pollutant up-to-standard emission of sludge recycling industry in China.

Recycling of Fenton sludge containing Ni as an efficient catalyst for tetracycline degradation through peroxymonosulfate activation

Fe sludge containing heavy metal Ni was used as a catalyst to activate potassium peroxymonosulfate (PMS) after thermal treatment. The crystal structures of recycled Fe sludge samples occur in the form of α-Fe2O3 and γ-Fe2O3. The existence of Ni had minimal effect on the crystal structure, but it changed the surface morphology and the internal chemical bond. X-ray photoelectron spectroscopy result proved that Ni existed as Fe–O–Ni. Influencing factors, such as the Ni content, PMS dosage, pH level, and the structural characteristics of the recycled products were explored. All the recycled Fe sludge products with and without Ni possessed catalytic activity in the removal of antibiotic tetracycline from the water for PMS activation. The optimal application conditions and possible mechanisms were proposed in accordance with the physicochemical properties of recycled products and the experimental results. Electron spin resonance spectra showed that Ni-containing Fe sludge could activate more OH· and SO4·− than the product without Ni. OH· and SO4·− are probably the critical free radicals in tetracycline degradation, but Ni did not significantly affect the catalytic degradation of tetracycline. Based on the findings of this study, the new idea and direction for the utilization of Fenton sludge can provide reference for heavy metal sludge recycling.

Evaluation of the factors limiting biogas production in full-scale processes and increasing the biogas production efficiency

Biogas production from sewage sludge volatile solids (VS) by anaerobic digestion slows down towards the end of the process, among inhibitory factors being pH increase upon ammonia accumulation, poorly digestible biomaterials, and high fixed solid (FS) content. The possibility of concentrating the digested sludge VS (41.7–56.6% on a dry weight basis) by surface and bottom layer separation with biogas post-production was studied. Furthermore, the potential to recycle concentrated VS and digested sludge back to the process after adjusting pH 7.0 to optimal for biogas-producing microbes and after acid, alkali, thermal, and sonolytic treatments was examined. In general, pH 7.0 control alone improved biogas production from the recycled digested sludge the most. An equally good improvement in biogas production was achieved by recycling the digested sludge, which had been heated until ammonia had evaporated and the pH dropped to 7.0 (1–2 h, 75 °C), and at the same time, VS was degraded. The biogas production from the sonicated and recycled sludge was almost as good as from the pH-adjusted, or heat-treated recycled sludge. After the acid and base treatments of the digested sludge, the recycled sludge yielded often the lowest biogas volume, as the added chemicals increased the FS concentration, which proved to be a more important inhibitory factor than poorly degradable VS. The high FS content significantly reduced the benefits of the treatments. By separating the surface and bottom layers with biogas post-production, the surface layer of VS was concentrated to 51.6–61.8%, while different compositions of the layers affected the biogas production.

A comparative study of waste activated sludge conditioning with Fe(II)-peroxymonosulfate oxidative process

Improving sludge dewaterability is a key step of waste sludge recycling. The effect and mechanisms on two kinds of waste activated sludge (WAS) with Fe(II)-peroxymonosulfate (PMS) oxidation were compared. For WAS-A, the optimum capillary suction time (CST) and specific resistance to filtration (SRF) reduction rates were achieved (56.5% and 89.3%, respectively) with PMS 0.1 g/g TSS and Fe(II) 0.05 g/g TSS. For WAS-B, the optimal results were PMS 0.1 g/g TSS and Fe(II) 0.1 g/g TSS, and the reduction in CST and SRF was 64.6% and 90.1%, respectively. After conditioning, the particle size decreased slightly while the zeta potential increased dramatically. The proteins and polysaccharides analysis indicated the destruction in extracellular polymeric substances (EPS) and microbial cells resulted from the sulfate radicals. Microtopography showed that the original structure was changed with irregular pores formed on the surface, thus facilitating the passage of internal water and further improving the sludge dewaterability.

Recycling of titanium-coagulated algae-rich sludge for enhanced photocatalytic oxidation of phenolic contaminants through oxygen vacancy

In the 21st century, sludge disposal and resource recycling are global issues. Titanium coagulation has received increasing attention due its strong coagulation capability and sludge recycling. Titanium coagulation is highly efficient for the treatment of algae-laden micro-polluted surface water; however, the safe disposal of titanium-coagulated algae-rich sludge remains a challenge. Here, we report on the recycling of titanium-coagulated algae-rich sludge for the production of functional TiO2 nanoflowers (TNFs) through a simple hydrothermal and calcination process. Anatase TNFs (particle size of 10–15 nm) with petal-like structures (mesoporous), relatively high specific surface areas, i.e. 299.4 m2g-1, and low band gaps, i.e. 2.67 eV (compared to P-25), were obtained. Additionally, oxygen vacancy (OV) was generated on the surface of the recycled TNFs based on electron paramagnetic resonance (EPR) results, which were verified by the first-principles calculations within density-functional theory. These TNFs display high photocatalytic performance for the degradation of diverse phenolic organic contaminants, such as bisphenol A, diphenyl phenol, p-tert-butyl phenol, and resorcinol, i.e. > 95%, under mild ultraviolet light irradiation and without any sacrificial reagents. Formation of OV on TNFs not only efficiently inhibited the recombination of photo-generated electrons and holes but also facilitated contaminant adsorption and photo-generated electron transfer on the surface of the recycled TNFs, thereby promoting the generation of holes and hydroxyl and superoxide radicals which were regarded as the reactive oxygen species for attacking contaminants in the reactions. This study proposes a new perspective on recycling chemical-coagulated sludge for producing functional nanomaterials as photocatalysts.

A mixture of sewage sludge and red gypsum as an alternative material for temporary landfill cover

This study proposed the recycling of sewage sludge (SS) and red gypsum (RG) as potential temporary landfill cover materials. Mixtures with different SS and RG compositions were prepared and tested in determining the most suitable design mix based on the resulting physical, mechanical, and geotechnical properties, namely the hydraulic conductivity, compressive strength, and plasticity. A maximum compressive strength of 524 kPa was achieved for the optimum SS:RG composition of 1:1, corresponding to Ca:Si composition of 2.5:1, which was appropriate to form the calcium silicate hydrate (CSH) gel. The SS and RG compositions did not affect the hydraulic conductivity, which was in the order 10−5 cm/s for all mixtures. Mixtures with RG greater than SS in composition exhibited plastic behaviour due to the Fe content in the RG, which helped minimize the risk of cracking. The optimum mixture had compressive strength greater than the specified minimum of 345 kPa, medium hydraulic conductivity, and moderate plasticity, thus appropriate for application as an alternative material for the temporary landfill cover in the tropics.

Potential Recovery of a Textile Wastewater Treatment Plant Sludge Into Clay Bricks

As the country started to become an export oriented country since the early 1970s, the growth of Malaysia’s textile industry has increased greatly. In 2011 alone, the country has provided a total of RM10.8 billion of exports of textile products and RM 6.6 billion of imports. This valuable improvement has lead to several environmental impacts involving land and water pollution. The current trend in waste management is to examine the feasibility of using textile sludge generated in wastewater treatment plants of textile industry as a partial replacement for clay as building materials. The chemical and physical properties of clay and textile have been analyzed. The effects of sludge proportion (0%-10%), and firing temperature (950oC and 1180oC) on the quality of the clay bricks were examined. The tests were conducted as per British Standard (BS) codes to investigate the potential of the textile sludge to be incorporate into clay for use as engineering blocks and load bearing bricks. According to the results, sludge addition and firing temperature are the important factors to determine the quality of clay bricks. All clay samples satisfied the requirement of British Standard norms in term of compressive strength and water absorption. It is seen that all bulk density of clay samples did not comply with good quality of clay brick but they can be categorized as lightweight building materials. Textile sludge was also tested for substitution into cement bricks. Cement samples with 10% textile sludge substitution comply with the requirement of British Standard norm for load bearing class 3. In summary, this study provides a preliminary research output that will contribute to expand a new area of research in recycling of textile sludge.

Waste-to-Carbon: Is the Torrefied Sewage Sludge with High Ash Content a Better Fuel or Fertilizer?

Sewage sludge (SS) recycling is an important part of the proposed ‘circular economy’ concept. SS can be valorized via torrefaction (also known as ‘low-temperature pyrolysis’ or ‘roasting’). SS can, therefore, be considered a low-quality fuel or a source of nutrients essential for plant growth. Biochar produced by torrefaction of SS is a form of carbonized fuel or fertilizer. In this research, for the first time, we tested the feasibility of torrefaction of SS with high ash content for either fuel or organic fertilizer production. The research was conducted in 18 variants (six torrefaction temperatures between 200~300 °C, and three process residence times of 20, 40, 60 min) in 5 repetitions. Fuel and fertilizer properties and multiple regression analysis of produced biochar were conducted. The higher heating value (HHV) of raw SS was 21.2 MJ·kg−1. Produced biochar was characterized by HHV up to 12.85 MJ·kg−1 and lower H/C and O/C molar ratio. Therefore, torrefaction of SS with high ash content should not be considered as a method for improving the fuel properties. Instead, the production of fertilizer appears to be favorable. The torrefaction increased C, N, Mg, Ca, K, Na concentration in relation to raw SS. No significant (p < 0.05) influence of the increase of temperature and residence time on the increase of biogenic elements in biochar was found, however the highest biogenic element content, were found in biochar produced for 60 min, under the temperature ranging from 200 to 240 °C. Obtained biochars met the Polish regulatory criteria for mineral-organic fertilizer. Therefore SS torrefaction may be considered a feasible waste recycling technology. The calculation of torrefaction energy and the mass balance shows energy demand <2.5 GJ∙Mg−1 w.m., and the expected mass yield of the product, organic fertilizer, is ~178 kg∙Mg−1 w.m of SS. Further investigation should consider the scaling-up of the SS torrefaction process, with the application of other types of SSs.

Microscopic analysis and mechanical properties of Recycled Paper Mill Sludge modified asphalt mixture using granite and limestone aggregates

As a developing nation that moves towards the sustainability, initiatives had been taken to address the solid waste disposal problem by incorporating them into asphalt pavement construction. This study integrates the recycled material named Recycled Paper Mill Sludge (RPMS) into the production of asphalt mixture as modifier through the partial substitution of mineral filler. The usage of solid waste material in pavement construction could substantially reduce the waste production and reduces the possibility of those waste materials ending up on landfills. This paper evaluates the microscopic analysis such as XRD, XRF and the mechanical properties of asphalt mixture with the incorporation of Recycled Paper Mill Sludge (RPMS). Mechanical properties that were evaluated were indirect tensile strength (ITS), moisture sensitivity, resilient modulus, Leutner shear and dynamic creep. RPMS was added to the asphalt mixture through dry process at the rate of 0.5% and 1%. Addition of RPMS at specific rate improved the mechanical properties such as resilient modulus, Leutner shear and dynamic creep of asphalt mixture. The lapped antenna like fibre of RPMS improved the resilient modulus of asphalt mixture by acting as a reinforcing material. Furthermore, RPMS contains calcite compounds that promote the adhesion bonding between asphalt binder and aggregates which significantly improved the performance in Leutner shear test and dynamic creep test.

Using recycled chemical sludge as a coagulant aid in chemical wastewater treatment in Mobarakeh Steel Complex

Coagulation–flocculation is a process commonly applied to treat many types of industrial wastewater. However, chemicals used in a wastewater treatment plant, including coagulants/flocculants, are costly. This study evaluated the feasibility of recycling the chemical sludge of the Mobarakeh Steel Complex (MSC), and using it as a coagulant aid in the process of wastewater treatment. The experiments were conducted in a jar test apparatus in consecutive cycles by adding a fraction of the settled sludge to samples. The response surface methodology (RSM) was employed to design the experiments and optimize the process. The response in the RSM model was residual turbidity, and the factors affecting the response included the sludge recycle ratio and return sludge cycle number. The sludge volume index (SVI) of the chemical sludge was also examined in each cycle of the tests to assess the sludge quality. The results revealed that recycling the sludge reduced the use of chemicals up to 60%. Finally, it was concluded that flocculation sludge could be considered as an alternative to chemicals, without adversely affecting the removal efficiency. Furthermore, SVI results showed that an increase in the number of cycles led to a decrease in SVI in each cycle, resulting in sludge volume reduction, better dewatering, and decreased sludge treatment costs.

An eco-friendly novel technique for power generation utilising municipal waste water and sludge recycling

Presently world is in need of more energy and drinking water due to the increase in population, industrialisation and urbanisation. Conventional sources of energy are limited, non-renewable, and health hazardous. There are verities of power plants, like thermal, hydro, wind, etc., running all around the world, however they need large infrastructure, create ecological imbalance and waste a lot of energy in form of heat, sound, etc. The present work aims to combine various power plants in a single unit system, utilising the waste energy loss, resulting augmentation in the efficiency of plant. It reduces the energy losses and provides pure drinking water from the municipal waste water. It solves the problem of solid waste treatment, because the domestic solid waste materials have been utilised to generate valuable products like oil, charcoal etc. along with power. It works continuously throughout the year, reduces infrastructures, as well as economical and eco-friendly too.

An eco-friendly novel technique for power generation utilising municipal waste water and sludge recycling

Presently world is in need of more energy and drinking water due to the increase in population, industrialisation and urbanisation. Conventional sources of energy are limited, non-renewable, and health hazardous. There are verities of power plants, like thermal, hydro, wind, etc., running all around the world, however they need large infrastructure, create ecological imbalance and waste a lot of energy in form of heat, sound, etc. The present work aims to combine various power plants in a single unit system, utilising the waste energy loss, resulting augmentation in the efficiency of plant. It reduces the energy losses and provides pure drinking water from the municipal waste water. It solves the problem of solid waste treatment, because the domestic solid waste materials have been utilised to generate valuable products like oil, charcoal etc. along with power. It works continuously throughout the year, reduces infrastructures, as well as economical and eco-friendly too.

Biogas and methane production efficiency of sewage sludge supplemented with conductive materials

Biogas production is one of the methods used in the recycling of sewage sludge which is a major problem for wastewater treatment plants to dispose. Methane is the most valuable content of biogas obtained from an anaerobic digestion (AD) process for energy production and accounts its 60%-70% when the AD process is operated efficiently. Recently, researches have focused on accelerating this process and obtaining much more methane content from different wastes. For this purpose, various conductive materials are used in the AD process to accelerate electron transfer between bacteria populations. In this study, granular activated carbon (GAC) and magnetite (Fe3O4) nanoparticles coated with pectin were used to determine their effects on the biogas and methane production from sewage sludge. Laboratory-scale fermentation reactors were used, and the highest biogas production and its methane content (%) were determined in the sample containing of 2.0 g-PNC/gVSS as 554.3±5.5 mL/g-dw, and 43.5±0.3%, respectively.

«St. Petesrburg Vodokanal» Experience in Developing Water Disposal Facilities as the Steps towards Transition to the Best Available Techniques

The article presents the case study of wastewater disposal facilities development performed by the State Unitary Enterprise ‘Vodokanal of St. Petersburg’ which is regarded as one of the ‘green cases’ being implemented in the Russian Federation. It was emphasized that the Vodokanal of St. Petersburg ‘green case’ holds both sectoral and regional significance. Authors discuss approaches towards development and stage-by-stage implementation of reconstruction and modernization programs as to existing treatment facilities and for designing new ones. The implementation stages are considered from the standpoint of improving the environmental and technological policy of the enterprise. The implementation results for modern wastewater treatment techniques (mainly concerning nitrogen and phosphorus removal) are presented. The company’s experience on operating wastewater sludge incineration installations is described. The article demonstrates an urgent need for a detailed analysis of technological and economic risks and opportunities during strategic planning and designing St. Petersburg Water Supply and Disposal Scheme due to the transition to new BAT-based technological regulation in the field of environmental protection. The role of the best available techniques in fulfilling the requirements of the Convention on the Protection of the Marine Environment of the Baltic Sea Region (HELCOM) is emphasized. Authors describe technical solutions implemented by the State Unitary Enterprise ‘Vodokanal of St. Petersburg’ which allowed to remove the enterprise from HELCOM environmental «hot spots» list. Approaches towards further activities on sewage sludge and ash recycling are presented. The article formulates recommendations on improving BAT-related regulatory legal acts based on the results of the case study and notes the expediency for developing a national strategy in the field of using sewage sludge as a secondary resource.

Modification of the cement stone active silm of urban treatment facilities

The use of recycled sludge from wastewater and products based on it in concrete is caused by an increase in the production of activated sludge in cities of millions and the restriction of free land for its disposal. The main components of activated sludge and fiber are SiO2, CaO, Al2O3, Fe2O3, MgO and P2O5, which allow the pozzolanic mechanism to manifest itself in a hardening cement matrix. Thus, activated sludge and fiber can be used as a modifier of the structure of hardening concrete. The use of municipal wastewater treatment plants in the production of building materials reduces the cost of waste disposal, social tension and solve problems related to environmental protection.

Evaluation of Toxicity of Paper Mill Sludge to Honey Bees and Analysis of Volatile Organic Compounds

Large amounts of sludge produced by paper mill industries represent one of the most serious environmental problems in the world. Recently, beekeepers living in the neighborhood of the paper mill in Hwasan County, Youngcheon city, GB, Korea, became alarmed that honey bee colonies were dying off suddenly across the neighborhood. A preliminary study was conducted to evaluate the toxicity (oral, fumigation, repellent) of recycled solid paper mill sludge (SPMS) and leachate paper mill sludge (LPMS) to honey bee workers under laboratory conditions, and to analyze the volatile organic compounds (VOC). The SPMS and LPMS were separately subjected to a liquid-liquid extraction (LLE) at three temperatures to extract VOC (highest VOC yields: 1.52% SPMS and 0.34% LPMS). A total of 70 chemicals were detected in the VOC of paper mill sludges, of which 49 and 21 volatile organic compounds from SPMS and LPMS, respectively. The SPMS was dominated by high degree presence of stanols (saturated sterols), such as cholestanol, cholestan-3-ol and also saturated hydrocarbons. However, LPMS was characterized by the absence of sterols. Both SPMS and LPMS showed an influence on the olfactory behavior of honey bee on Y-tube assay, with repulsion rates of 72 and 68%, respectively. Both SPMS and LPMS at concentration of 100 mg/mL caused higher honey bee oral mortality than the untreated controls at 48, 72, 96 and 120 hours after treatment (highest oral mortality at 120 hr: 85.74% (SPMS); 93.51 % (LPMS)). A similar pattern was observed when honey bees were tested to fumigant toxicity. Both SPMS and LPMS caused significant higher mortality than the untreated control 24 hour after the exposure (highest fumigation mortality at 120 hr: 69.4% (SPMS); 56.8% (LPMS)). These preliminary results indicated that paper mill sludge could be partly responsible for sudden death and disappearance of honey bees, especially in hot humid summer days. With climate change, the risk of environmental chemical exposure to honey bee would pose greater attention.