Dry Sludge Research Articles

Effect of cold plasma on breaking activated sludge and the output dominance of protein

ABSTRACT Upon contacting with water, cold plasma should produce numerous ozone molecules and free electrons at room temperature. In this study, a cold plasma generator was used to break the walls of residual activated sludge obtained from domestic sewage. The impact was mainly influenced by the ozone generated. With 800 W power, sludge wastewater pH of 12.0, and under continuous treatment for 10 h, the system’s reduction efficiency for the dry sludge was ≈90%. Furthermore, the organic matter content (especially protein) of the upper layer of the sludge solution increased a lot after the sludge digestion. This observation proved the reduction of sludge from both sides. Moreover, when the cold plasma technique was compared with thermal acid hydrolysis, thermal alkali hydrolysis, and ultrasonication for extracting protein from activated sludge, cold plasma wall-breaking sludge exhibited the highest efficiency, reaching 38.2% under ambient temperature. After the analysis, the toxic metal content in the extracted protein was near zero, which is a level other protein extraction methods via sludge breaking have not achieved to date, we attribute this efficiency to free electrons the cold plasma produce. These species promote the transformation of metal ions into atomic metals, thereby facilitating their removal.

Use of ballasted flocculation (BF) sludge for the manufacturing of lightweight aggregates

Ballasted flocculation (BF) is an efficient way to remove the turbidity from surface water. The objective of the present study is to optimize the ballast (magnetite), coagulant (poly aluminum chloride) concentration and pH for efficient turbidity removal from surface water. To do this, the sludge produced from an optimized dose of a BF treatment was utilized for the production of lightweight (LW) aggregates by combining it with hard clay and sewage sludge. The LW aggregates were formed by means of rapid sintering in the temperature range of 1000–1200 °C with an exposure time of 10 min. The physical properties of the LW aggregates, in this case the leaching of heavy metals, the bulk density and the microstructure, were investigated. The results indicated that corresponding ballast and coagulant concentrations of 0.75 g/L and 30 mg/L (poly aluminum chloride (PAC)) resulted in the maximum removal efficiency of ≈95%. Using a mixture of BF sludge (30 wt%), dry sewage sludge (20 wt%), and hard clay (50 wt%), aggregates with a density of around 1.0 g/cm3 could be produced. In addition, it was confirmed that the manufactured aggregate was environmentally stable as the elution of heavy metals was suppressed.

A comprehensive study of the high temperature pyrolysis of sewage sludge: kinetics, energy analysis and products formation

<p>This study evaluates the pyrolysis of sewage sludge until 960 °C using heating rates between 3 K/min and 12 K/min in a macro TG/EGA. Mass and energy balances and kinetic parameters are determined. Thermal decomposition is divided into a low temperature zone (until 550 °C to 590 °C), for decomposition of organic matter, and a high temperature zone, for decomposition of inorganic matter and secondary reactions of the residual organic matter. In dry basis at 570 °C solid, liquid and gaseous products amount to 69.2 wt.-%, 29.2 wt.-% and 1.6 wt.-%, respectively. An increment in the final temperature to 960 °C causes a successive decrease of the solid residue to 56.9 wt.-%. The solid product contains more than 80 wt.-% mineral matter with high amounts of valuable elements, such as Ca and P. An energy requirement of 2.18 MJ/kg of dry sewage sludge is calculated for the pyrolysis until 570 °C. At this temperature, 58.5 % of the energy entering the process is concentrated in the liquid product and 40.0 % in the solid. A suitable set of kinetic parameters is determined through a formal independent parallel reactions model with six-pseudo components, using a combination of isoconversional and fitting methods.</p>

Drying and energy recovery of sludge

Drying and energy recovery of sludge

Evaluation of Physical and Chemical Properties of Poultry Sludge and its Suitability for Reuse in Agricultural and Non-Agricultural Applications

Disposal of poultry sludge is one of the great challenges facing cities because of very strict requirements for landfilling and the scarcity of space for landfills. The present study was therefore aimed at evaluating the physical and chemical properties of poultry sludge and its suitability for reuse in agricultural and non-agricultural applications. Three samples were collected from sludge at the wastewater treatment plant of Al-Thuraya slaughterhouse in Al-Mafraq District, Jordan. The physical and biochemical properties of these samples were analyzed. Also, elemental composition and heat value were determined. The results indicated that poultry sludge had a slightly alkaline pH and a total moisture content of 20%, as well as an average total solid of 80%. The dry solid sludge had a volatile solid content of 94.9% and 5.1% of ash. Also, dry sludge had a high protein content (62 %) followed by carbohydrate (20%) and fiber (17%), with fat being around 1%. The major elements in the sludge were carbon (65.5%) followed by nitrogen (16%), phosphorous (5 %) and sulfur (2%). Heavy metal concentrations in dry sludge ranged from 0.01 to 2 mg/kg. These heavy metal concentrations were well below the safe limits recommended by legislators for sludge used as a fertilizer. The findings from this study revealed that dry poultry sludge offers a wide range of potential uses as fertilizer, animal feed and a source of energy, and it should be considered as a potentially valuable and sustainable resource rather than a waste product.

Effects of Air Temperature and Humidity on the Kinetics of Sludge Drying at Low Temperatures

In this study, a low-air temperature sludge drying system was constructed and the effects of temperature and relative humidity on the characteristics of the system were investigated. The results showed that the drying rate of sludge increased with an increase in air temperature and a decrease in the air’s relative humidity. The influence of temperature on the average drying rate exhibited an approximate quadratic distribution, while the influence of relative humidity on the average drying rate exhibited an almost linear distribution. The relationship equations of the average drying rate, temperature, and humidity were summarized and compared with the experimental results, and the maximum relative error was 7.6375%. By comparing the experimental results with the commonly used thin-layer drying models, it was found that the sludge drying characteristics were more consistent with the Midilli model. Based on the relevant parameters of the Midilli model, the relationship between the segmented drying moisture content and the average drying rate was proposed, and the empirical formula of the drying rate and MR under different conditions was fitted.

Impact of dry sewage sludge on characteristics of concrete

Nowadays, the accumulation of various waste products is increasing day by day. So there is a great need for their proper disposal, without harming the environment. Moreover, due to the limited availability of natural resources like fine aggregates. There is a need for alternative building materials. The study's primary goal was to find an alternative, effective disposal method of dry sewage sludge of wastewater treatment plants as a building material. The possibility of using dry sewage sludge in concrete was assessed in this study. Various properties, like workability, compressive strength, ultrasonic pulse velocity, split tensile strength, water absorption, and cost-benefit analysis were reported in the study. According to the study, utilizing 5% of dry sewage sludge as a fine aggregate is possible without having a significant negative influence on concrete characteristics. With the use of dry sewage sludge, the manufacturing cost of concrete can be reduced by1.63%.

Recycling biochar derived from tannery liming sludge for chromium adsorption in static and dynamic conditions

In tannery industry, unhairing and liming (termed as liming) are indispensable but it is a very polluting part of process when producing quality leather. Expelled wastewater from liming generates significant amounts of liming sludge. In this study, efficacies of liming sludge biochar derived for adsorption of chromium from tannery wastewater are described. The biochar was characterized by FTIR, SEM, EDX, and BET technologies, and pHzpc. Surface area and responsible functional groups of biochar were as follows: 9.2 m2/g and C-H, C-N, C-O, C=C, N-H, S=O, and O-H. EDX analysis revealed chromium adsorption and SEM images led to changes in surface morphology. pHzpc for dry liming sludge and biochar were 4.1 and 6.1, respectively. Batch adsorption was verified by assorted parameters including biochar dose, shaking speed, contact time, and dilution factor. Column study results confirm the highest chromium adsorption efficiencies of 408.12 and 533.41 mg/g for 3 cm and 5 cm bed height, respectively. Regression coefficient suggested that adsorption obeys the Freundlich isotherm and pseudo-second order kinetics in batch mode, while it follows the Yoon–Nelson model in column mode. The physicochemical parameters of tannery wastewater prior and post-adsorption revealed good removal efficiencies for chloride content (Cl), chemical oxygen demand (COD), and biochemical oxygen demand (BOD) were, respectively, 50.5%, 80.1%, and 85.5%. Desorption process recovers 69.37 mg/g Cr from adsorbed biochar which could be reused in the tanning process. Consequently, an innovative state-of-the-art tannery liming sludge biochar can satisfactorily use in tannery wastewater treatment by following wealth-from-waste principle.

Deep dewatering of activated sludge using composite conditioners of surfactant, acid and flocculant: The mechanism and dosage model

To address the problem of difficult disposal caused by poor dewaterability of high-organic sludge in wastewater treatment plant, this study developed a sludge composite conditioner (SCC) consisting of sodium dodecyl sulfate (SDS), HCl and FeCl3. It has the potential to significantly improve the dewaterability of the high-organic sludge with the VSS/MLSS of 80%. The moisture content (MC) and bound water content of sludge were reduced from 98.00 to 59.65% and from 3.42 to 0.91 g/g dry sludge (DS) after being conditioned, respectively. The surfactant (SDS) promoted the dissolution of extracellular polymeric substances (EPS). The acid (HCl) enhanced the decomposition of the sludge flocs, making the insoluble EPS peel off and turn into the liquid phase. As a result, total EPS decreased by 52.70% compared to the original sludge. In addition, due to the neutralization effect of protons and FeCl3, the Zeta potential increased remarkably from −13.80 mV to −1.72 mV and the dispersed sludge particles formed during EPS dissolution process were re-flocculated, which increased the average size of the sludge particles. The ratio of proteins (PN)/polysaccharides (PS) also increased from 1.69 to 3.81. And a quantitative model of optimum dosage of SCC agents based on the influence of the sludge PS, PN and EPS content has been established, aiming to determine the dosage of each conditioner according to the properties of target sludge. In general, the SCC provided an effective pathway for sludge deep dewatering.

Mainstream double-anammox driven by nitritation and denitratation using a one-stage step-feed bioreactor with real municipal wastewater

A novel double-anammox process for advanced mainstream nitrogen removal was established using step-feed sequencing batch reactor (SBR) system with integration of suspend sludge and biofilms. Following optimization of influent distribution ratio, the effluent total inorganic nitrogen (TIN) was < 10.2 mg N/L, with influent TIN of 43.4 mg N/L, and anammox contributed 71.4% to TIN removal. Biological processes and batch tests revealed that gradient C/N reduction promoted denitratation/anammox in anoxic stage, and simultaneous nitritation and anammox were achieved in oxic stage. Specially, anammox maintained on biofilms with abundance over 109 copies/ (g dry sludge). High-throughput sequencing revealed that Thauera and Nitrosomonas were enriched in flocs. Furthermore, metagenomic sequencing confirmed that Thauera owns narG and napA (NO3–→NO2–) and Nitrosomonas owns amoA (NH4+→NO2–), support stable NO2– supply for double-anammox. This mainstream anammox-dominant process could potentially be used for stable nitrogen removal in municipal wastewater treatment plants.

Production of biochar from the combination of foaming drying and pyrolysis of sludge with the additive of Camellia oleifera shell biochar

In this study, a combination of foaming drying and pyrolysis of sewage sludge (SS) with the additive of Camellia oleifera shell biochar (COSC) process was performed to investigate the effects of process parameters on the foaming drying process, and the properties of the produced biochar. The physical and chemical properties of the products were analyzed and the produced biochar was characterized by FTIR, XPS, and XRD analyses. The produced bio-oil was analyzed by gas chromatography-mass spectrometer (GC–MS). Foamed sludge mixed with Camellia oleifera shell biochar (250−850 μm) (COSC-FS) has a higher drying efficiency. Compared with the dried SS, the dried foamed sludge (FS) has lower HHVs, C, H, N, O content, and higher ash content. The main component of bio-oil was nitrogen-containing aliphatic compounds. Though having a lower specific surface area than unfoaming pretreatment, the biochar obtained from the pyrolysis of foamed sludge mixed with Camellia oleifera shell biochar (COSC-FSC) still has a higher adsorption ability for Pb(II) due to co-precipitation. The addition of NaOH had no effect on the pH of solution from Pb(II) adsorption by COSC-FSC. The adsorption behavior of Pb(II) adsorbed onto the COSC-FSC can be well described by pseudo-second-order kinetic model and Langmuir isotherm model with the improved maximum adsorption capacity of 179.33 mg/g. This work provides a promising method for the disposal and the resource utilization of sludge.

Sensitivity Analysis of the Climate Effect of Using Pyrochar Biofuel for Heat and Electricity Generation

This study aims to quantify the climate change impact of pyrochar production from pulp and paper mill sludge and the subsequent utilisation in combined heat and power (CHP) plants for co-generation of heat and electricity using the environmental life cycle assessment (E-LCA) method. In the Pyrochar Scenario, in which the sludge is pyrolyzed into pyrochar, the authors have assumed that pyrochar would replace coal. In the Reference Scenario, sludge is incinerated with a subsequent low rate of energy recovery. A comprehensive sensitivity analysis was performed to determine the conditions in which the sludge pyrochar would offer the greatest climate-effect benefits. The parameters selected for the said analysis are the form of pyrochar (pellet or powder), fuels replaced by it in the CHP plant (solid waste and peat vis-à-vis coal), and the utilisation of the pyrochar fuel in another European country (Germany and Spain vis-à-vis Sweden). The results of this E-LCA clearly show that using pyrochar as a biofuel in CHP plants delivered a considerable reduction in greenhouse gas (GHG) emissions (−1.87 tonne CO2-eq per 2.8 tonne dry sludge). Contribution analysis reveals that the process accounting for the biggest share of the reduction is the pyrochar combustion (a negative contribution of 76%), which results in a displacement of coal-based fuels. The authors conclude that the utilisation of pyrochar in firing units would provide the highest reduction in GHG emissions, while recommending a comprehensive economic analysis in addition to climate effect assessment, before making a decision regarding the introduction of sludge pyrochar to the energy sector.

Microbial community dynamics and electricity generation in MFCs inoculated with POME sludges and pure electrogenic culture

Palm Oil Mill Effluent (POME) requires treatment before disposal due to its high organic matter content. In this study, the electrical performance and wastewater treatment efficiency were evaluated for Microbial Fuel Cells (MFC) treating unsterile POME with chemical oxygen demand (COD) from 200 to 10 000 mg/L. Since the inoculum type is a key factor in MFC performance, three types of sludge (methanogenic sludge (MS), facultative sludge (FS), and dry sludge (DS), obtained from the current POME treatment ponds were evaluated as inoculum. Dry sludge (DS) developed a maximum power output of 3.30 W/m3 by oxidizing 71% out of the COD provided by POME (1000 mg/L). Also, raw POME microbiota contributed to an enrichment of the community in DS inoculum along with the operation, in which Geobacter was the predominant genus reaching a current generation of 247 mA/m2 and a power density of 2.36 W/m3. Conversely, pure electrogenic (Shewanella sp.) inoculation led to a diversification process, resulting in a lower current generation of 52 mA/m2 and a power density of 0.10 W/m3. Consequently, microbial community dynamics revealed that MFC inoculation tends to a microbial equilibrium wherein generation of high current density was achieved by gradual microbial enrichment rather than external electrogenic invasion.

Strength and durability of dry sewage sludge (DSS) as a replacement for fine aggregates

Sewage sludge disposal has become a challenging task in India. Central Pollution Control Board of India in 2011 stated that around 10.7 million tons of dry sewage sludge (DSS) is being disposed every year. Generally sewage sludge is disposed by means of incineration, buried in underground pits, disposed into water bodies and used in agricultural lands. These methods lead to air pollution, enhancing global warming through rising atmospheric temperature and affecting the environment's cleanliness. In this study, DSS is introduced in concrete as a replacement for fine aggregates (5, 10, 15 and 20%). All the concrete mixes were tested for its properties such as compressive strength, split tensile strength, flexural strength, abrasion resistance, impact resistance and durability properties in aggressive conditions like acid attack, and effect of sea water. Results reveal that up to 10% DSS incorporation has enhanced compressive strength by 9% and replacements till 15% enhanced flexural and split tensile strength up to 13%. In case of durability properties, incorporation of DSS up to 15% showed better results than control concrete in terms of acid attack, effect of sea water, abrasion resistance and impact resistance. Cost analysis indicated that DSS can reduce up to 2.5% of cost considering the efficacy of compressive strength.

Utilization of wastewater sludge for lightweight concrete and the use of wastewater as curing medium

The increasing population have resulted in a higher generation of domestic and industrial wastewater sludge. The sludge ends up as a landfill in designated areas which makes the land unusable. The search for lightweight materials for construction has led to the use of sludge as a viable replacement for the basic composition of concrete due to its low density. The dry sludge collected from Polokwane Waste Water Treatment Works (WWTW) in Limpopo Province was used as a partial replacement of sand in concrete. The sludge content in the sand was varied from 2.5, 5, 7.5, 10, to 12.5 %. The outcomes of the analysis indicate that the partial replacement of sand with dry sludge in the concrete mix is viable and useful. The result showed that up to 7.5 % of sand could be replaced with dry sludge in concrete for structural applications. Also, wastewater can be used as a curing medium. The unit weight of the concrete decreased with increasing sludge content, which was attributed to the lower density of the sludge. The SEM image revealed a porous nature and irregular surface morphology of the sludge and the concrete.

Effect of sintering temperature and dwelling time on the characteristics of lightweight aggregate produced from sewage sludge and waste glass powder

Present study aims to explore the effect of sintering temperature and dwelling time on the characteristics and morphological structure of lightweight aggregates made from dry sewage sludge and waste glass powder. The mixtures were sintered at temperatures from 1100 °C to 1200 °C at a heating rate of 10 °C/min with a dwelling time of 10, 20, and 30 min to produce lightweight aggregate samples. The thermophysical behavior of the mixtures and the physic-mechanical properties (including water absorption, particle density, and compressive strength) of the obtained lightweight aggregates were studied. The microstructure of the lightweight aggregates was also analyzed using X-ray micro-computed tomography. Results indicate that increasing the sintering temperature or extending the dwelling time will reduce the particle density and compressive strength of lightweight aggregates. Moreover, the sintering temperature and dwelling time show a considerably influence on the pore structure of lightweight aggregates, which is strongly related to the physical characteristics of the lightweight aggregates. The lightweight aggregates obtained at optimized sintering temperature of 1180 °C with an optimal dwelling time of 10 min show water absorption of 1.01%, particle density of 0.78 g/cm3, and compressive strength of 7.10 MPa, thereby meeting the standard requirement of GB/T 17431.2–2010.

Improving performance and efficiency of partial anammox by coupling partial nitrification and partial denitrification (PN/A-PD/A) to treat municipal sewage in a step-feed reactor

Improving contribution and nitrogen removal efficiency (NRE) of partial anammox in municipal wastewater is a researching hotspot. This study developed an innovative PN/A-PD/A process with fixed biocarriers in anaerobic/anoxic chambers for actual sewage treatment in a typical step-feed reactor over 390 days. Two coupled pathways providing continuous NO2– (partial nitrification in oxic chambers and partial denitrification in anaerobic/anoxic chambers) for anammox were introduced to the process, achieving 47% nitrogen loss by anammox in stable phase. The influent and effluent total inorganic nitrogen (TIN) were 51.3 and 11.0 mg/L, respectively, even with chemical oxygen demand (COD)/TIN ratio of 2.9. Anammox activity improved from 6.52 to 9.68 mg NH4+-N/gMLSS/d and abundance on the biocarriers raised to 3.16 × 1010 gene copies/g dry sludge. Overall, this study confirmed partial anammox, spatially coupled with partial nitrification and partial denitrification via oxic/anoxic distribution with step feed mode, as an alternative for application of mainstream anammox.

Microplastics in an agricultural soil following repeated application of three types of sewage sludge: A field study

Microplastics were investigated in an agricultural soil to which three types of sludge were repeatedly applied: fresh municipal sludge (FSS1), fresh mixed sludge (mainly industrial sludge) (FSS2), and dry heat-treated municipal sludge (DSS). The percentages of microplastics <1.0 mm were 24.3 and 28.7–59.1 % in unamended and amended soils, respectively. Particles of this size accounted for 47.1–60.0 % of microplastics in different sludges and polymers of particle size <100 μm occurred in all soil samples and sludges examined. Fibers were the commonest microplastic type, ranging from 66.7 to 82.5 % in soil and 89.4–97.2 % in sludges. Polyester (PES) and polypropylene (PP) accounted for ~80 % of the total microplastics found in soil and poly-(styrene:acrylate) (PS-AC) microspheres were found in all sludge-amended soil samples examined. There was also a pronounced weathering effect on the surfaces of the microplastics in soil. Nine years of repeated sludge application led to the accumulation of microplastics in the soil. The abundance of microplastics was significantly higher in the municipal sludge (149.2 ± 52.5 particles kg−1) than in the mixed (68.6 ± 21.5 particles kg−1) or dried (73.1 ± 15.4 particles kg−1) sludge and this was related to the microplastic abundance in the sludges. This field study confirms that sludges are drivers of soil microplastic pollution and measures are required to minimize the inputs of microplastics to agricultural land.

Computational modeling of biosludge drying

Considerable increases in industrial and urban wastewater sludge generation in recent years require proper treatment, such as thermal drying, and disposal. The sludge drying is a complex process involving simultaneous and coupled heat and mass transfer, which can be modeled by taking into account mass and heat balances, and assuming that water diffuses according to kinetic laws. This research implemented a simulation model for biosludge drying processes to predict the temperature and moisture distribution inside the biosludge, using the COMSOL Multiphysics® simulation program v5.2. A parametric analysis was carried out to determine the effect of initial moisture content on biosludge final temperature and moisture reduction. The simulated temperature and moisture content were experimentally validated and good agreement was observed between the simulation and experimental results. This model is a useful tool to optimize the drying process and develop better strategies for the control of the system.

Model-Based Evaluation of Hydrothermal Treatment for the Energy Efficient Dewatering and Drying of Sewage Sludge

This research paper evaluates hydrothermal carbonization (HTC) as a possible treatment for sewage sludge, including phosphorus recycling. German governmental requirements force a high number of wastewater treatment plants (WWTP) to recover phosphorus from sewage sludge above limits of 20 g kgTS−1 before further disposal (e.g., co-incineration). The results show that pH reduction has a positive effect on shifting phosphorus to the liquid phase during HTC. Although the experimental results of this research do not yet achieve the necessary phosphorus reduction, various calculations are made to achieve this goal in future experimental studies. In order to be able to assess the energy benefits of HTC, Aspen Plus modeling was used to show the positive impact of implementing this technology in a WWTP. It is shown that the mechanical dewaterability of sewage sludge (SS) increases after HTC enabling energy savings by means of subsequent thermal drying. A heat optimized HTC is able to cut energy expenses by half, further providing a phosphorus-depleted hydrochar for extensive energetic use.