Recycling Of Sludge Research Articles

Extensive Green Roof Substrate Composition Based on Sludge Recycling

The experiment was carried out to study the reasonable composition of stable anaerobic sludge in the extensive green roof growth substrate by a total of 650 mm artificial rainfall event. Combined with the N, P leaching problem of the sludge resources utilization, the quality of the effluent and the change of the nutrient content of the substrate in the process of application were investigated. The results showed that the anaerobic sludge could significantly increase the plant biomass and the average weight gain was 808%. Stable anaerobic sludge caused a large amount of leaching of TP and water treatment residual could effectively control TP leaching and did not affect the absorption of P to the plant. During the experiment, the TP of the effluent was reduced by 68.66%.After stabilization, the effluent TP reached the surface water Ⅴ standard. The main form of leached TN was NO3--N and the leaching of NO3--N could be reduced by rice husk charcoal. In the experiment, the NO3- -N leaching mass was reduced by 28.86% totally. Increasing the amount of rice husk charcoal helped to control NO3--N leaching. SS and COD could be quickly decreased and stabilized. The COD of effluent after stabilization was about 30 mg·L-1, which was better than the standard of surface water Ⅴ. Under the condition of actual precipitation with medium and small rainfall, the anaerobic sludge nutrient retention time should be more than 1 year, which meets the growing needs of plants for a long time.

Screw pyrolysis technology for sewage sludge treatment

Sewage sludge quantities have grown continuously since the introduction of the European Directive (UWWTD 91/271/EEC) relating to the treatment of urban wastewater. In the present, most of the sewage sludge is combusted in single fuels incineration plants or is co-fired in waste incineration or coal power plants. The combustion of sewage sludge is a proven technology. Other treatments, such as fluidized bed gasification, were successfully adopted to produce suitable syngas for power production. Besides, the number of large wastewater treatment plants is relatively small compared to the local rural ones. Moreover, alternative technologies are arising with the main target of nutrients recovery, with a special focus on phosphorus. The aforementioned issues, i.e. the small scale (below 1MW) and the nutrients recovery, suggest that pyrolysis in screw reactors may become an attractive alternative technology for sewage sludge conversion, recovery and recycling. In this work, about 100kg of dried sewage sludge from a plant in Germany were processed at the newly developed STYX Reactor, at KIT. The reactor combines the advantages of screw reactors with the high temperature filtration, in order to produce particle and ash free vapors and condensates, respectively. Experiments were carried out at temperatures between 350°C and 500°C. The yield of the char decreased from 66.7wt.% to 53.0wt.%. The same trend was obtained for the energy yield, while the maximum pyrolysis oil yield of 13.4wt.% was obtained at 500°C. Besides mercury, the metals and the other minerals were completely retained in the char. Nitrogen and sulfur migrated from the solid to the condensate and to the gas, respectively. Based on the energy balance, a new concept for the decentral production of char as well as heat and power in an externally fired micro gas turbine showed a cogeneration efficiency up to about 40%.

Effect of Recycle Sludge on Anaerobic Digestion of Palm Oil Mill Effluent in A Thermophilic Continuous Digester

The objective of this research is to maintain short retention time and high degradation of palm oil mill effluent (POME) to biogas by applying recycle sludge. Fresh POME from Rambutan Mill without further treatment was used as feed. Two lab-scale digesters supported from Metawater Co. Ltd. have been applied to treat POME at thermophilic (55°C) condition. Both digesters were operated under intermittent operation mode. Experiments were performed in two methods: with and without recycle sludge. Hydraulic retention time (HRT) of both methods was maintained at 6 days, while sludge retention time (SRT) was maintained at various days. The result showed that by extending SRT in return sludge process where 25% of digested slurry recycled to the digester, improvement of volatile solid (VS) decomposition was obtained around 84% at HRT of 6 days and SRT of 21 days. Then, chemical oxygen demand (COD) removal efficiency could be reached until 85% by using recycle sludge.

Asymptotic Behavior of a Chemostat Model with Constant Recycle Sludge Concentration.

In this work, we study a several species aerobic chemostat model with constant recycle sludge concentration in continuous culture. We reduce the number of parameters by considering a dimensionless model. First, the existence of a global positive uniform attractor for the model with different removal rates is proved using the theory of dissipative dynamical systems. Hence, we investigate the asymptotic behavior of the model under small perturbations using methods of singular perturbation theory and we prove that, in the case of two species in competition, the unique equilibrium which is positive is globally asymptotically stable. Finally, we establish the link between the open problem of the chemostat with different removal rates and monotone functional responses, and our model when two species compete on the same nutrient. We give some numerical simulations to illustrate the results.

Sorptional dehydration and thermochemical sintering of converter sludge

Global steel output in 2016 exceeded 1.6 billion t, of which more than 1.2 billion t was produced in converters. The smelting of 1 t of steel produces up to 25 kg of fine dust, depending on various factors. This dust contains up to 65% iron, in oxide form. Recycling of the waste formed in steel production costs half or a third as much as the preparation of ore concentrates. For the recycling of converter sludge, methods of conditioning wet wastes by isothermal sorptional dehydration and subsequent thermochemical sintering have been developed. The adsorbent used in the present work is the solid residue from lignite pyrolysis: fine-grain lignite semicoke produced by a pilot plant at the Berezovskii-1 mine. The lignite-semicoke samples produced have a highly developed pore structure and correspondingly are characterized by excellent sorptional and energy properties. The granulometric composition of lignite semicoke is practically the same as that of the sludge. At the same time, the density of the lignite-semicoke particles is 2.5 times less than that of the sludge particles, even when the pores of the semicoke are completely filled with adsorbed moisture. On mixing the lignite semicoke and converter sludge, the semicoke absorbs moisture. The resulting mixture is highly friable, whereas the moisture adsorbed in the pores passes to the bound state and becomes an active participant in redox processes. As a result of the experiments, new material containing up to 39% Femet and 49% C is obtained. On that basis, an effective technology may be developed for the utilization of converter sludge to produce ferrocoke that may be employed as a fuel and reducing agent in blast furnaces and smelters. The proposed technology does not require complex mechanical and thermal dehydration and briquetting with binder.

Effectiveness of sewage sludge ash combined with waste pozzolanic minerals in developing sustainable construction material: An alternative approach for waste management

Utilization of the sewage sludge ash in fabricating the construction material would be an effective alternative approach under the sludge management scheme other than landfilling. The present investigation deals with the utilization of the recycled sewage sludge ash (SSA) combined with the quicklime (QL) and blast furnace slag (BFS) as a cementitious material in controlling the physical and mechanical performances of mortar. The mortar samples were prepared using the different amount of SSA, QL, BFS, and alkali activator (AA). The performance of the sewage sludge ash based mortar (SAM) was evaluated measuring the bulk density, apparent porosity, compressive strength, flexural strength, and shrinkage strain, etc. The result reveals that the higher dose of AA (50% weight w.r.t the volume of water used) and QL (20% w.r.t. weight of the total cementitious material) influences the mechanical strength of SAM. Additionally, the optimum dose of the BFS (10% w.r.t. weight of the total cementitious material) leads to yield a maximum compressive strength (31.3 MPa) of SAM. Finally, based on the analytical analysis, a model has been proposed to explain the overall performance of the SAM. Hence, the utilization of SSA (70%) combined with QL (20%) and BFS (10%) for the fabrication of mortar and concrete is assumed to be an effective alternative technique in developing sustainable construction material and waste management as well.

A Pilot Study of the Sludge Recycling Enhanced Coagulation–Ultrafiltration Process for Drinking Water: The Effects of Sludge Recycling Ratio and Coagulation Stirring Strategy

The pilot-scale study on a sludge recycling enhanced coagulation–ultrafiltration (UF) process for surface water treatment is investigated in this paper. The impact of the sludge recycling ratio and coagulation stirring strategy on removal, sedimentation efficiency, and membrane fouling control was studied in this work. Sludge recycling ratios of 0%, 5%, 10%, 15%, and 20% were applied, and the optimal ratio was found to be 10%. Moreover, four stirring strategies were also applied, and the best stirring strategy for coagulation was found to be rapid mixing (velocity gradient: 280 s−1), which is quite different from the coagulation stirring strategy without sludge recycling. This suggests that the adsorption effect of sludge could play a leading role during the procedure. Moreover, shortening the coagulation process makes it possible to reduce energy consumption.

Continuous sulfidogenic wastewater treatment with iron sulfide sludge oxidation and recycle

This study evaluated the technical feasibility of packed-bed sulfidogenic bioreactors dosed with ferrous chloride for continuous wastewater treatment over a 450-day period. In phase I, the bioreactors were operated under different combinations of carbon, iron, and sulfate mass loads without sludge recycling to identify optimal treatment conditions. A COD/sulfate mass ratio of 2 and a Fe/S molar ratio of 1 yielded the best treatment performance with COD oxidation rate of 786 ± 82 mg/(L⋅d), which resulted in 84 ± 9% COD removal, 94 ± 6% sulfate reduction, and good iron retention (99 ± 1%) under favorable pH conditions (6.2–7.0). In phase II, the bioreactors were operated under this chemical load combination over a 62-day period, during which 7 events of sludge collection, oxidation, and recycling were performed. The collected sludge materials contained both inorganic and organic matter with FeS and FeS2 as the main inorganic constituents. In each event, the sludge materials were oxidized in an oxidizing basin before recycling to mix with the wastewater influent. Sludge recycling yielded enhanced COD removal (90 ± 6% vs. 75 ± 7%), and better effluent quality in terms of pH (6.8 ± 0.1 vs. 6.5 ± 0.2), iron (0.7 ± 0.5 vs. 1.9 ± 1.7 mg/L), and sulfide-S (0.3 ± 0.1 vs. 0.4 ± 0.1 mg/L) removal compared to the baseline operation without sludge recycling during phase II. This process exhibited treatment stability with reasonable variations, and fairly consistent sludge content over long periods of operation under a range of COD/sulfate and Fe/S ratios without sludge recycling. The bioreactors were found to absorb recycling-induced changes efficiently without causing elevated suspended solids in the effluents.

Investigation and recycling of paint sludge with cement and lime for producing lightweight construction mortar

Since paint sludge (PS) consists of many toxic substances, it has high pollution potential. Incorrect disposal of the significant amount of PS threats to public health and the environment, especially in developing countries. The present research reveals investigation of construction materials production from recycled PS as an aggregate replacement. In this study, PS has been obtained from white goods industry. Various PS content has been used in both cement and lime separately then physical and mechanical properties have been investigated in the hardened condition. Interestingly, all specimens have demonstrated unexpected expansion in compare with the pure matrix at curing periods. Although adding PS to cement (PS-cement) and to lime (PS- lime) result with the relative decrease in strength; based on the obtained results, the final structure has a promising characteristic potential for lightweight residential construction materials. Besides, it has thermal and sound insulation properties due to high expansion and high porous content with reducing sources of toxics entering to environment.

Process for Dewatering of Water-Containing Oil Sludge

There was considered a scheme of formation, recovery and involvement in the production of oil sludge. There were outlined the most widely used combination of methods of disposal and recycling of oil sludge and negative consequences of the use of watered fuels for heat and power equipment. For efficient dewatering of water-containing waste oil there was offered a method of dewatering on the basis of low-grade waste heat boiler heat transfer. The final dehydrated product may be used as additives for boiler fuel without substantially reducing of thermo technical characteristics of the combustion process.

Effect of Blast Furnace Sludge (BFS) Characteristics on Suitable Recycling Process Determining

The present study aims to give a detailed characterization of blast furnace sludge (BFS) by using different techniques, in order to determine the most effective recycling method to recover valuable metals from this waste. BFS is composed mainly of hematite, as its iron-bearing phase, and carbon, in addition to fractions of silicate and carbonate materials. The studied BFS shows relatively high contents of iron (Fe) (390 g.kg-1), and carbon (C) (290 g.kg-1), due to abundance of hematite and coke, while the concentration of zinc (Zn) (2.5 g.kg-1) is low. The XRD analyses indicated that, hematite is more concentrated in the fine fraction (<20 μm), while the coarser fraction (90 - 250 μm) is dominated by calcite, quartz and X-ray amorphous coke. SEM-EDX analyses confirmed that particles rich in iron and zinc were detected in the fine fraction (<20 μm) of the sludge. Due to high Fe and C content in BFS, it can be utilized as self-reducing material and briquetting represent a potential method for recycling of blast furnace sludge.

Basic scheme of copper and zinc waste recycling in metallurgical brass production

The article proposes a recycling scheme for dusty waste generated during the metallurgical brass production with the use of two-stage leaching. During the first stage, when the dust is dissolved by a 0,5 mol/l sulfuric acid solution, a product solution containing the major amount of zinc ions (0,46 mol/l) and a small amount of copper ions (less than 0,02 mol/l) is obtained. Copper is sequentially electrochemically isolated from this solution, at a current density of 0,1 A/dm2, and then zinc is isolated at 5,0 A/dm2. The dry residue (cake) is subjected to copper-ammonia leaching, as a result of which all copper passes into the solution, and associated metals remain undissolved. In order to extract copper from the resulting solution, the liquid extraction by a 0,34 mol/l DH-510A solution in kerosene is used. Copper ions are extracted from the organic phase through re-extraction by a 2,0 mol/l sulfuric acid solution. The cathode copper is extracted from the obtained sulfuric acid electrolyte at current density of 1,5–2,0 A/dm2. The advantages of the proposed scheme are the increase in environmental friendliness through the use of solution recirculation at all stages of the process, as well as waste minimization through the entire process of dusty metallurgical sludge recycling.

WASTE ACTIVATED SLUDGE AS ALTERNATIVE FUEL FOR ENERGY AND RESOURCE CONSERVATION

The paper deals with the energy and resource conservation using waste as an alternative fuel. The object of the study is waste activated sludge which is formed at biological wastewater treatment plants and is stored on sludge lagoons that leads to the alienation of large land areas. For the waste activated sludge recycling, its preliminary dehydration is required because of its high water cut. Dosing the carbonate sludge formed at thermal power plants at the stage of liming and coagulation of natural additional water is suggested to increase the efficiency of dewatering of waste activated sludge by centrifugation. After mechanical dehydration by pelletizing with a binder, fuel pellets, which can be used as an alternative fuel to generate heat and electricity, are produced. According to the results of the study, lignosulfonate – a technical by-product of the woodworking industry – is chosen as the most effective binder. The paper presents an elemental analysis of fuel pellets, as well as their heat of combustion, and proposes a technological scheme including the following components: mechanical dewatering (centrifugation), drying, pelletizing and incineration of waste (the incineration takes place in a fluidized bed furnace). The use of fuel pellets based on waste activated sludge and water treatment sludge makes it possible to efficiently utilize waste from industrial petrochemical and heat energy complexes and to switch from traditional energy resources to renewable ones.

Encouraging “K” strategy nitrifiers over “r” strategists in bioaugmentation reactor

Bacteria responsible for ammonia oxidization (AOB) can be differed into two groups which have different bio kinetic parameters. Those groups are slow growing bacteria with lower half saturation coefficient for NH4 (k -strategist) and fast growing bacteria with higher half saturation coefficient for NH4 (r- strategist). By controlling operational conditions of process it is possible to create dominance of one of those colonies to enhance the nitrification rate. Therefore model of sequencing bath reactor was developed to study the correlation of bioaugmentation of the side stream breeder reactor and predominant AOB culture. The course of the study was to find the minimal bioaugmentation influent of AOB rich recycled sludge to create dominance of k-strategist in the side stream reactor with maintaining maximal possible increase of overall AOB load. In addition operating conditions like sludge retention time, NH4 concentration and loading regimes was investigated to determine the optimum for the process.

Future proof decentralised sludge recycling Elodry-pro®

Abstract At Linz-Unkel (Germany) sewage treatment plant the first full scale state-of-art EloDry-Pro® plant for sewage sludge has been constructed, consisting of the PYREG® reactor and the EloDry® belt dryer. The system is characterised by small footprint, flexibility, modular design and efficient energy management. The sludge dried using an EloDry® belt dryer undergoes staged combustion using the PYREG® module at around 6,500°C. This reduces the sludge to a fraction of its original volume while disinfecting it and removing micro-pollutants such as pharmaceutical residues. The residual ash, which has a high percentage of plant-available phosphorus, is then supplied to the fertiliser industry as a recycled raw material. The working principle of EloDry-Pro® installation, including heat flows of the system, is presented. The paper describes Pyreg®'s advanced emission control systems, preventing NOx formation and removing harmful substances such as mercury and sulphur. The EloDry-Pro® technology is an innovative and cost-effective approach to decentralised thermal recycling of sewage sludge. Both sewage sludge volumes and transportation costs are reduced by up to 90%, therefore making it a low carbon cost-effective alternative to the transportation of sludge and allowing local sludge processing at plants under 100 k population.

Long-Term Impact of Field Applications of Sewage Sludge on Soil Antibiotic Resistome.

Land applications of municipal sewage sludge may pose a risk of introducing antibiotic resistance genes (ARGs) from urban environments into agricultural systems. However, how the sewage sludge recycling and application method influence soil resistome and mobile genetic elements (MGEs) remains unclear. In the present study, high through-put quantitative PCR was conducted on the resistome of soils from a field experiment with past (between 1994 and 1997) and annual (since 1994) applications of five different sewage sludges. Total inputs of organic carbon were similar between the two modes of sludge applications. Intrinsic soil resistome, defined as the ARGs shared by the soils in the control and sludge-amended plots, consisted of genes conferring resistance to multidrug, β-lactam, Macrolide-Lincosamide-Streptogramin B (MLSB), tetracycline, vancomycin, and aminoglycoside, with multidrug resistance genes as the most abundant members. There was a strong correlation between the abundance of ARGs and MGE marker genes in soils. The composition and diversity of ARGs in the five sludges were substantially different from those in soils. Considerable proportions of ARGs and MGE marker genes in the sludges attenuated following the application, especially aminoglycoside and tetracycline resistance genes. Annual applications posed a more significant impact on the soil resistome, through both continued introduction and stimulation of the soil intrinsic ARGs. In addition, direct introduction of sludge-specific ARGs into soil was observed especially from ARG-rich sludge. These results provide a better insight into the characteristics of ARG dissemination from urban environment to the agricultural system through sewage sludge applications.

Titanium tetrachloride for silver nanoparticle-humic acid composite contaminant removal in coagulation-ultrafiltration hybrid process: floc property and membrane fouling.

Titanium-based coagulation is expected to achieve both efficient water purification and sludge recycling. This study is the first attempt to use titanium tetrachloride (TiCl4) for silver nanoparticle (AgNP)-humic acid composite contaminant removal in a coagulation-ultrafiltration (C-UF) process, where characterization of flocs and membrane fouling under varied coagulant dose, initial solution pH, and AgNP concentration conditions are the main contents. Results suggested that the TiCl4 achieved high AgNP removal in the form of silver nanoparticle through adsorption and sweep flocculation and simultaneously exerted additional 68.2% higher dissolved organic carbon removal than Al2(SO4)3. The TiCl4 produced larger and stronger flocs but with weaker recoverability and less compact degree than did Al2(SO4)3. Floc properties were independent of AgNP concentration except floc fractal dimension, which was negatively correlated with AgNP concentration. The TiCl4 precoagulation caused less membrane fouling within wider pH range than Al2(SO4)3 did in the C-UF process. Incorporation of AgNPs during the TiCl4 pretreatment process facilitated the mitigation of membrane fouling, which was, however, negligibly influenced by AgNP concentration in the case of Al2(SO4)3.

Concentration of Nitrate in Main Anoxic Stage and PHA, TP Metabolism for Nitrogen and Phosphorus Removal in Single Sludge System with Continuous Flow

Based on test results and mass balance, PHA, TP metabolic regularity was revealed under different nitrate nitrogen concentrations in main anoxic stage [c(NO3)] for nitrogen and phosphorus removal in single sludge system with continuous flow, then the effectiveness of using c(NO3) as control parameter was proved from the perspective of the reaction mechanism. During experiment period, the influent COD, total nitrogen (TN), and total phosphorus (TP) concentrations were stabilized at (285.78±18.19), (58.13±3.79), and(7.14±0.51) mg·L-1, respectively. The experiment was carried out under the condition that the c(NO3) values were 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 mg·L-1 based on the feedback control structure using PLC automatic control system to control the nitrifying liquid flow with the water quality. The sludge load of COD was (0.253±0.071)kg·(kg·d)-1, the sludge load of TP in anaerobic stage was (0.006±0.001) kg·(kg·d)-1, the sludge load of TN in aerobic stage was (0.049±0.006) kg·(kg·d)-1, the hydraulic retention time (HRT) in bioreactor was 9h, the sludge recycle flow was 0.5, and the mixed liquor recycle was 1.0. The results showed that effect of c(NO3) value on PHA synthesis and storage rate in the ANS was conspicuous, and the percentage of PHA storage occupied 74% of COD removal when c(NO3) value was 2.5 mg·L-1.The impact of c(NO3) value on PHA degraded in the main anoxic stage was great, and the percentage of PHA degradation in the main anoxic stage occupied 55% of total PHA degradation when c(NO3) value was 2.5 mg·L-1. The phosphorus released in anaerobic stage changed along with increasing c(NO3), and the amount of phosphorus released obtained the maximum value 6.16 g·d-1 when c(NO3) value was 2.5 mg·L-1. In addition, under c(NO3) value of 2.5 mg·L-1, the amount of total phosphorus uptake and anoxic phosphorus uptake obtained the maximum values of 8.04 g·d-1 and 3.67 g·d-1, respectively. Then it was confirmed thatc(NO3) could serve as a run controlling parameter with the best value of 2.5 mg·L-1 from the perspective of PHA and TP metabolic mechanism.

Pilot-Scale Operation of a Concrete Sludge Recycling Plant and Simultaneous Production of Calcium Carbonate

A pilot-scale plant to treat concrete sludge and produce calcium carbonate (CaCO3) and an environmental purification agent (phosphorus adsorbent derived from concrete sludge, PAdeCS®) was designed, constructed, and operated. Concrete sludge from a concrete pile and pole production plant, boiler gas containing CO2, and groundwater were used in the plant. The process involved calcium extraction from concrete sludge into water, followed by reaction of the calcium with CO2 to produce crystalline CaCO3. The pilot-scale plant was operated for 1 week, and the mass flows, conversion of CO2 to CaCO3, and net CO2 emissions of the process were estimated. High-purity CaCO3 (>97%) suitable for industrial use was obtained. Based on the power consumption of the process and the amount of CO2 sequestered into CaCO3, a net reduction in CO2 emissions can be achieved using this process. The produced PAdeCS can be used as an inexpensive substitute for calcium series environmental purification agents.

Pollutant removal characteristics of a two-influent-line BNR process performing denitrifying phosphorus removal: role of sludge recycling ratios.

This paper studied denitrifying phosphorus removal of a novel two-line biological nutrient removal process treating low strength domestic wastewater under different sludge recycling ratios. Mass balance of intracellular compounds including polyhydroxyvalerate, polyhydroxybutyrate and glycogen was investigated together with total nitrogen (TN) and total phosphorus (TP). Results showed that sludge recycling ratios had a significant influence on the use of organics along bioreactors and 73.6% of the average removal efficiency was obtained when the influent chemical oxygen demand (COD) ranged from 175.9 mgL-1 to 189.9 mgL-1. The process performed better under a sludge recycling ratio of 100% compared to 25% and 50% in terms of ammonia and COD removal rates. Overall, TN removal efficiency for 50% and 100% sludge recycling ratios were 56.4% and 61.9%, respectively, unlike the big gap for carbon utilization and the TP removal rates, indicating that the effect of sludge recycling ratio on the anaerobic compartments had been counteracted by change in the efficiency of other compartments. The higher ratio of sludge recycling was conducive to the removal of TN, not in favor of TP, and less influence on COD. Thus, 25% was considered to be the optimal sludge recycling ratio.