Sludge Mass Research Articles

Investigating chemical changes, material properties, and off-gas emissions in sewage sludge through thermal plasma treatment.

This study aimed to investigate the thermal plasma treatment of sewage sludge as an alternative waste management solution. Samples were collected from a sewage treatment facility in São Paulo, Brazil, and subjected to thermal treatments in a furnace at temperatures of 400, 600, 800, and 900°C to assess moisture content, mass loss, and ash composition. Subsequently, the samples were processed in a thermal plasma reactor operating at an average power of 30kW. Comprehensive characterization using X-ray fluorescence, X-ray diffraction, and Fourier-transform infrared spectrometry revealed the presence of oxides, particularly those of K, Ca, and Fe, which influence material melting points. Plasma treatment significantly reduced the mass and volume of the sewage sludge, losing up to 72 and 90%, respectively. Gas analysis indicated syngas (CO+H2) production with a high heating value (HHV) of 9049kJ/m³, underscoring the energy recovery potential. Leaching and solubility tests confirmed the treated material as inert and suitable for safe disposal or reuse in construction, with chemical and structural analyses showing that the vitrified material was primarily composed of SiO₂. These findings highlight the effectiveness of thermal plasma treatment in achieving sustainable sewage sludge management by combining waste reduction, energy recovery, and the production of environmentally safe by-products.

Enhancing fish sludge bioconversion kinetics for nutrient recovery in aquaponics using a modified biological aerated filter with a novel media of polyhedral hollow spheres.

Nutrient recovery from aquaculture sludge is vital for promoting hydroponic plant growth and achieving near-zero solid waste discharge in aquaponic systems. Modified biological aerated filters (MBAFs) are promising because of the dual capabilities of aquaculture sludge collection and aerobic mineralization. However, the bioconversion kinetics, which is indirectly related to the packed media, need to be improved. In this study, a novel polyhedral hollow sphere (PHS) medium was used in an MBAF (MBAF-PHS) to overcome the shortcomings of the current medium, facilitating fish sludge retention and enhancing subsequent bioconversion kinetics for nutrient recovery. An average rate of 36.9g/d for dry weight of fish sludge was achieved during 29d of filtration and an average reduction rate of 31.30g/d during 26d of bioconversion. The total mass of fish sludge was converted by 76.2% via the co-action of the solubilization of organic solids and degradation of dissolved organic matter. MBAF-PHS was competitive for macronutrient recovery compared with the MBAF-sponge previously used. The ratios of the final concentrations of the macronutrients (P, Mg, and S) to the concentrations in Hoagland solution (Cf/CH, %) were 278.1, 162.8, and 200.9%, respectively, whereas the ratios of N, K, and Ca were 65.9, 37.1, and 51.0%, respectively. High bioconversion kinetics of NO3--N and PO43--P were obtained within 7d with an MNO3-N/MTN of 79.9% and MPO4-P/MDTP of 80.3%. The nutrient bioconversion of fish sludge was associated with the diversity of the microbial community in the MBAF-PHS, especially the population of nitrogen-removing microbial species that developed after 9d of mineralization.

Reducing sludge formation by enhancing biological decay of biomass: a mathematical model

Abstract We investigate a model for an activated sludge process that contains a chemical reactor unit attached to a bioreactor. Inside the chemical reactor unit, a process takes place which increases the decay coefficient of heterotrophic biomass. This mimics a number of experimental techniques which are used to decrease the mass of sludge. Such techniques are of growing interest as the activated sludge process produces large volumes of sludge; the costs associated with its disposal are significant. Our primary interest is to investigate how the operation of the chemical reactor unit changes the steady-state concentrations of both the total suspended solids within the biological reactor and the chemical oxygen demand in the effluent stream. The operation of a chemical reactor unit always increases the value of chemical oxygen demand in the effluent stream. The behaviour of the total suspended solids is more complicated; in some cases, the operation of the CRU increases the total suspended solids. For a fixed value of the chemical oxygen demand in the influent stream, we show that both the percentage reduction in the total suspended solids and the chemical oxygen demand in the effluent stream are increasing functions of the soluble substrate in the feed. The same trends occur when the influent composition is fixed, and the disintegration rate inside the chemical reactor unit is increased. This leads to dichotomic behaviour, decreasing the total suspended solids increases the chemical oxygen demand in the effluent stream. There are two consequences of this behaviour. Firstly, there are some waste streams that can not be cleaned using the process configuration considered in this paper. Secondly, the imposition of a target value for the chemical oxygen demand in the effluent stream imposes a maximum achievable reduction in the total suspended solids in the biological reactor. Higher reductions can not be achieved without causing the chemical oxygen demand in the effluent stream to exceed the target value.

The Use of Papaya Seeds (Carica papaya L.) as a Biocoagulant in the Dairy Industry Liquid Waste Treatment Process with the Coagulation-Flocculation Method

Dairy industry discharges wastewater characterized by high values of Total Suspended Solid and turbidity. The waste is commonly processed using chemical coagulants which negatively impact human’s health and the environment. Papaya seeds can be used as a coagulant as their positively charged proteins that can bind the negatively charged particles allowing the resulting floc to settle and clear water to be obtained. The goals of this study are to determine the characteristics of the dairy industry wastewater before and after flocculation coagulation, the characteristics papaya seed biocoagulant, the effect of the biocoagulant’s dosses, particle sizes, and stirring speed on the turbidity and the Total Suspended Solid of the dairy industry wastewater, and the performance of the biocoagulants in processing the dairy industry waste using Sludge Volume Index and Sludge Mass. The treatments applied in this research are in terms of doses (250 mg, 500 mg, and 750 mg), particle sizes (60,120, and 230 mesh), fast stirring speeds (120 rpm, 180rpm, 200 rpm for 1 minute), and slow stirring speeds (10 rpm, 30rpm, and 50 rpm for 20 minutes) all of which were expected to reduce the waste’s turbidity and the number of Total Suspended Solid. This study finds that the treatment with the highest reduction of Total Suspended Solid is D3P3KP2, which decreased turbidity from 754 NTU to 92 NTU. The treatment with the highest reduction of Total Suspended Solid was D3P3KP2 which decrease the Total Suspended Solid from 124 mg/L to 79 mg/L. The performance of the papaya seed biocoagulant of D3P3KP2 treatment is considered good as the acquired highest value of the Sludge Volume Index is 83.13 ml/g and as the procured lowest value of the Sludge Mass is 81.48%.

Evaluation of the effect of using sewage sludge as a fertilizer on the concentration of heavy metals in soil and the economic implications of its application

The costs of fertilising the soil with sewage sludge were reduced to the operating time of the equipment and the working time of the labourers operating the equipment in the two main operations (manure spreading and ploughing), for three sewage sludge application doses, namely 50, 100 and 200 Mg·ha-1. The costs were calculated using the Katalog Nakładów Rzeczowych nr 2-21: Tereny zielone/Ministerstwo Gospodarki Przestrzennej i Budownictwa (2009) and the current prices from Sekocendbud (2023). The effectiveness of fertilisation was assessed by studying the level and change in heavy metal content after the soil was fertilised with sewage sludge at three proportional doses, namely 50, 100 and 200 Mg·kg-1. The sewage sludge used for fertilisation complied with the sanitary requirements for sludge to be utilised for natural purposes (Regulation, 2015). The estimated total cost of sludge application ranged from PLN 12646.19 to PLN 20456.73 per 1 ha for doses from 50 to 200 Mg per 1 ha. The results of the estimation confirmed the hypothesis that the unit cost of fertilisation with stabilised sewage sludge increases with the dose of sludge in relation to the area of fertilised soil and decreases with the increase of the mass of sludge deposited in the soil. Optimising fertiliser costs, therefore, requires selection - increasing the sludge dose per unit area. No contamination of the soil with copper, cadmium, lead and zinc was found despite an obvious increase in the content of these metals when mixed into the soil. The application of sewage sludge, even in multiple doses, did not result in exceeding the permissible limit for the content of these elements in the soil, as defined in the Minister of the Environment Regulation of 2015 (Regulation, 2015).

Heat and Mass Transfer Characteristics of Oily Sludge Thermal Desorption

Oily sludge is a loose material containing solid and multiple liquid components. Thermal desorption is an efficient method of disposing of liquids from oily sludge. Most existing studies have mainly discussed the effect of some external process parameters on thermal desorption, with little discussion on the heat transfer characteristics and the variation in the wet component mass of oily sludge under heating. Small-scale experiments have been performed to measure the rise in temperature and liquid phase content change of the sludge during heating. The temperature rise rate increases with material density and increases faster during the initial heating stage, while it slows down as the liquid phase evaporates. The adhesive shear stress is determined by measuring the pulling force of the test rod, which decreases with decreasing water content and increases significantly with decreasing oil phase content. Heat transfer and energy distribution models have been developed to calculate the rise in the temperature of materials and the evaporation of contained liquids. The heat and mass transfer processes are obtained from simulation calculations by taking the initial material with a mass content of 25% water and 10% oil under a heating temperature of 500 °C. When the heating time reaches 135 min, the drying region reaches the boundary of the test container, at which the material temperature exceeds 350 °C. During the evaporation of different liquid-phase components, there are multiple segments in the corresponding temperature curves. The processing time and heat source temperature can be reasonably determined by analyzing the temperature rise of the material, and the effect of the disposal of liquids from oily sludge can be predicted by analyzing the changes in liquid content. The results may guide the formulation of process parameters for engineering project schemes for oily sludge disposal.

Carbon content and other soil properties of near-surface peats before and after peatland restoration.

Peatland restoration usually aims at restarting the peatlands' function to store carbon within peat. The soil properties of the near-surface peat can give a first understanding of this process. Therefore, we sampled pH value, total organic carbon content (TOC), total nitrogen content (TN), C/N ratio as well as dry bulk density (BD), and describe the structure of near-surface peats in six restored fens in North-East Germany before (2002-2004) and after (2019-2021) restoration. Before restoration, the study sites showed peat degradation to various extents in their near-surface peats. pH values remained relatively stable over time. Comparing the degraded peat horizons, TOC increased significantly in four study sites, ranging from 35.7% to 47.8% in 2002-2004 and from 42.5% to 54.0% in 2019-2021. TN varied from 1.5% to 3.5% in 2002-2004 and from 1.8% to 3.2% in 2019-2021, but changes were only significant in one site, showing a slight decrease. In three sites, the increase in C/N ratio was significant, indicating lower nutrient availability. BD ranged from 0.08 to 0.48 g/cm3 in 2002-2004 and from 0.10 to 0.16 g/cm3 in 2019-2021, decreasing significantly in four sites. The structure of the degraded peat horizons changed after restoration to a more homogenous, sludge mass with larger re-aggregates. In three sites, new peat moss peat layers above the degraded soil horizon were present in 2019-2021, with a mean thickness of 6.8 to 36.1 cm. The structure was comparable to typical, slightly decomposed peat moss peat. Our findings suggest that within about 17 years after fen restoration, and thereby a water table rise close to surface, TOC of the near-surface peats increased to values that are typical for undisturbed peatlands. This indicates that restoration can lead to the re-establishment of peatlands as potential carbon sinks, with TOC within the near-surface peat as one key factor in this process. Further, we assume that the decrease in nutrient availability, decrease of BD, and new, undisturbed peat layers can favor the establishment of mire-specific biodiversity and support ecosystem services similar to near-natural mires.

Tannery sludge valorization through zeolite-assisted anaerobic process for short-chain fatty acids (SCFAs) production

Tannery sludge, a challenging waste, was utilized as a substrate for the production of Short-Chain Fatty Acids (SCFAs) through a series of six thermophilic Continuous Stirred-Tank Reactor runs. The sludge was subjected to a mild thermal pre-treatment and incorporated zeolites (chabazite in run II, and clinoptilolite in run III) in the acidification process. Results highlighted zeolites' impact on chromium concentration and the SCFAs/CODSOL ratio. Ammonia release remained consistent at around 47 % and 51 % for run I and II, respectively, but surpassed 60% in run III, suggesting limited zeolite effectiveness in NH4 absorption. Chromium release in the liquid fraction, due to thermal pretreatment, reached 335 mg/L. While in tests without zeolite, complete removal proved challenging, in zeolite-amended runs, complete removal was achieved, showcasing the materials' heavy metal absorption capacity. SCFA concentrations reached 20260 mgCOD/L, with acidification efficiency varying; runs I and III had ratios around 0.70 COD/COD, while run II showed substantial improvement (0.92) with chabazite. Anaerobic fermentation-digestion mass balance indicated a 41% reduction in landfill sludge mass, reducing its environmental footprint while yielding valuable byproducts like biogas and SCFAs. These findings underscore zeolites' potential in heavy metal absorption and acidification process enhancement, paving the way for applications with tannery sludge.

Disinfection of the water recovered from drying of aquaculture scallop sludge

A substantial volume of saline sludge with high water content is generated by the aquaculture industry, particularly during bivalve production. The reclamation of water from this sludge becomes particularly crucial in arid regions. This study is the first of its kind to focus on recovering water from sludge produced during the aquaculture of scallops and the subsequent disinfection of this water to remove heterotrophic microorganisms. The method employed involved a solar still followed by a condensation system for water recovery. We obtained 250 kg of wet sludge from the industrial production of scallop culture (Argopecten purpuratus) through the rotary drum filter, which is used for lantern washing. This sludge was subjected to drying in a solar still dryer. The vapor generated during the drying process was condensed using a heat exchanger, resulting in the recovery of 1680 mL of water, accounting for 91% of the sludge mass, with a Gain Output Ratio of 1.6. The recovered water underwent disinfection using various methods, including UV-A, UV-A/O3, UV-C, UV-C/O3, and O3. Among these, the UV-C/O3 process demonstrated the highest removal of Total Cultivable Bacteria, achieving complete disinfection within 60 min of treatment. UV-C was the second most effective treatment, with a bacteria removal rate of 99.92% in the same timeframe. Electrical energy used to reduce bacteria concentration by one order of magnitude was 12.96 kWh/m3 when UV-C process was applied, and 32.92 kWh/m3 when UV-C/O3 process was applied. In conclusion, this study showcases that a significant quantity of water can be reclaimed from scallop sludge through a combination of solar drying and a condensation system. Moreover, this recovered water can be efficiently disinfected using the UV-C/O3 process.

Performance of a continuous micro-oxygen up-flow sludge bed reactor for assimilation of partial nitrification/anammox sludge into a CANON granular-floc system

CANON process was established in a micro-oxygen up-flow sludge bed reactor through one-step inoculation of partial nitrification/anammox sludge. The process was divided into three stages according to the influent NH+4-N concentrations. The position of aeration played a vital role as low DO concentration and sludge loss showed evident negative effects. Placing the aeration device above the sludge bed significantly enhanced the stability of the system, and the DO concentrations were maintained between 0.4 and 0.8 mg/L. The total nitrogen (TN) removal efficiency reached ∼70% within 5 days in stage I, yet the reaction stoichiometric ratios deviated from theoretical values. As the activity of anaerobic anammox bacteria (AnAOB) exceeded ammonia oxidizing bacteria (AOB) in stage III, the maximum TN removal rate reached 350 mg N/ L·d and the TN removal efficiency was retained at a relatively high value of 83%. Flocculent sludge converged into a granular-floc hybrid system with the percentage of sludge mass for particle size between 0.4 and 1 mm increased from 0% to 43.48%, and the percentage of sludge mass for particle size between 0 and 0.2 mm remained at 22.76%. Following 135 days of continuous operation, an interaction balance between AOB and AnAOB was reached with high activities and dominant abundance while nitrite oxidizing bacteria (NOB) were suppressed.

Restructuring anaerobic hydrolysis kinetics in plant-wide models for accurate prediction of biogas production

In this study, the effect of anaerobic hydrolysis rate on biogas production was investigated with mesophilic digesters in seven large-scale wastewater treatment plants. A linear correlation was determined between the percentage of primary sludge mass in the total sludge fed to the digester and the overall anaerobic hydrolysis rate. The anaerobic hydrolysis rate of primary sludge was determined to be three times higher than that of biological sludge. The reduction factors for anaerobic hydrolysis (ηHYD,ana) were identified in the range of 0.11–0.30 which is lower compared to the recommended range (0.30–0.50) given in the literature. This study proposes a new model approach where anaerobic degradation kinetics of influent originated (XB) and decay originated (XB,E) particulate biodegradable organics are separated. Current plant-wide models with a single kinetic expression required recalibration of the model for calculating biogas flowrate for each treatment facility with different primary and secondary sludge ratios fed to the digesters. The new model structure is able to predict biogas production of all wastewater treatment plants without any recalibration effort by segregating degradation kinetics of two particulate biodegradable organic fractions (XB, XB,E).

Efficient purification of graphite industry wastewater by a combined neutralization-coagulation-flocculation process strategy: Performance of flocculant combinations and defluoridation mechanism

The wastewater generated by the graphite industry exhibits high acidity and contains elevated concentrations of toxic ions, posing challenges for its efficient and cost-effective treatment. This study presents a novel approach for treating graphite industry wastewater, involving a synergistic process that combines NaOH neutralization, Ca(OH)2 mid-stage coagulation, and compound agent flocculation. The results showed that when pH = 2 was adjusted with NaOH and continued to pH = 8 with Ca(OH)2, the amount of precipitation produced was 62% lower than that of the conventional Ca(OH)2 coagulation process. Based on the defluoridation mechanism, polyaluminum chloride sulfate (PACS) and poly(dimethyldiallylammonium chloride) (PDMDAAC) were identified as the best compound flocculants. The turbidity and fluoride removal efficiencies of raw water reached 99.37% and 99.80%, respectively, when the mass ratio was m(PACS:PDMDAAC) = 9:1, the stirring rate was 150 rpm, and the coagulant dosage was 170 mg/L. By using X-ray powder diffractometer (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) characterization, the flocculation-defluoridation mechanism of PACS in combination with PDMDAAC was examined for its synergistic effect. The flocculation-defluoridation mechanism confirmed that the adsorption complexation of Al3+ on F- is significant in the removal of low concentrations of fluoride ions. Practical applications have proved that this treatment strategy can effectively solve the problems of excessive sludge mass and low removal rate of fluoride and metal ions in graphite industrial wastewater treatment. This process provides a new idea to promote the application of combined flocculants in the large-scale treatment of industrial wastewater.

Effects of stabilizers on CO2 fixation capacity in neutralization of alkali construction sludge

Construction sludge, generated from tunneling and piling, is typically in a liquid state. It can be improved via physical treatments, such as dehydration, and/or chemical treatments, using stabilizers, in order to to be recycled as construction material. To adjust the strength of sludge, chemical treatments are often preferred. However, chemical treatments frequently result in alkali leaching. Methods to reduce alkalinity by curing the alkaline sludge under CO2 gas at a certain concentration have been proposed in Japan. In recent years, technologies that utilize CO2 to improve the quality of cementitious material have received considerable attention in terms of carbon capture. Therefore, the effects of stabilizers on the CO2 fixation capacity of alkaline sludge during pH neutralization were investigated in this study. Accelerated carbonation and carbonate content measurement tests were conducted to detect the CO2 content fixed in alkaline sludge specimens treated with various stabilizers. The test results showed that the fixed maximum CO2 content per gram of dry mass of sludge, (mCO2)max, increased with the calcium oxide (CaO) content of the stabilizer(s) per gram of dry sludge, CCaO. However, the rate of increase in (mCO2)max with CCaO was significantly affected by the type of stabilizer used. In the case of quicklime (QL), the ratio of (mCO2)max to CCaO was approximately 0.5, whereas, in the cases of fly ash (FA) and steel slag (SS), the ratio was approximately 0.25. The ratios for biomass ash and paper sludge ash were between that for QL and that for FA and SS. Detailed analyses of the test results suggest that the CaO content per gram of stabilizer(s) in the sludge, C*CaO, can provide an estimate of the fixed maximum amount of CO2 per gram of stabilizer(s) in the sludge, (m*CO2)max. However, other factors, including the amount of water-soluble Ca, should be considered for a precise evaluation. Additionally, the experimental results showed that the decrease in pH owing to neutralization increases with the increasing CCaO. However, the type of stabilizer did not significantly affect the relationship between the degree of CO2 fixation and the degree of neutralization.

Co-pyrolysis of peanut shell with municipal sludge: reaction mechanism, product distribution, and synergy.

Biomass/sludge co-pyrolysis contributes to the high-efficiency resource utilization, harmless treatment, and reduction in volume of sludge. Due to the complexity of co-pyrolysis reaction, it is essential to evaluate the thermodynamic behavior, synergy, and reaction mechanism of this process to make it commercially viable. In this work, the pyrolysis properties, thermodynamic analysis and product distribution of municipal sludge (MS), peanut shell (PS), and their blends with various sludge mass ratios (SMRs) were investigated by a thermogravimetric analyzer and a fixed bed reactor. There was a considerable synergy existing in the process of PS/MS co-pyrolysis, and the synergy occurred mainly at the devolatilization phase, accelerating the mixture pyrolysis. When the conversion rate α was less than 0.7, the apparent activation energy decreased continuously with SMR at the same α; however, it increased dramatically with SMR when α was greater than 0.7. Reactants and reaction stages greatly affected the kinetic mechanism of fuel pyrolysis, and this finding was beneficial for the numerical simulation of mixture pyrolysis. Based on the conclusions and precision of this work, the mass ratio of PS to MS was recommended to be 6:4, which had the strongest synergy, with a gas yield of 26.69 wt.% at 600°C and a lower heating value (LHV) of pyrolysis gas of 14.89 MJ/Nm3.

Sludge Reduction and Surface Investigation in Electrochemical Machining by Complexing and Reducing Agents

Electrochemical machining (ECM) is widely applied to manufacture parts with complex geometries, used in electronic components and the automotive, military, and aeronautics industries. These parts have a surface shaped by controlled anodic dissolution at high current density levels, using a neutral solution of inorganic salts (i.e., NaCl or NaNO3) as the electrolyte. Such conditions generate a high amount of sludge that deposits onto the surfaces of equipment, devices, cathodes, and working pieces, requiring daily and complicated sludge management during the series production in the industry. Thus, the main goal of the present work is to propose a simple way to reduce sludge generation in the ECM industrial process. To do so, complexing (EDTA) or reducing (ascorbic acid) agents were added to the electrolyte composition, creating parallel reactions to keep the metallic ions from precipitating. The complexing agent EDTA resulted in a 30% reduction in sludge mass, using an alkaline solution (pH > 10.0). The reducing agent, ascorbic acid, resulted in a 90% reduction in sludge mass, using an acidic solution (pH < 5.0). This sludge reduction has the potential to contribute significantly to increasing equipment, devices, and cathode lifetime, as well as reducing costs associated with centrifuge or filter maintenance (sludge removal from electrolyte) and increasing the productivity of industrial ECM processes.

Activity of Ammonium-Oxidizing Bacteria—An Essential Parameter for Model-Based N2O Mitigation Control Strategies for Biofilms

The reduction in N2O emissions is an important task in the control of wastewater treatment plants. Since local operating conditions, especially inside biofilms, are usually not known, models are an important tool in the development and implementation of control strategies. For a pilot-scale nitrifying biofilm reactor and an SBR, different operational strategies to reduce autotrophic nitrous oxide (N2O) formation were developed and tested by applying a combination of modeling and measurement. Both approaches highlighted the relevance of addressing the actual AOB activity as a sensitive control variable. The investigated strategies, therefore, focused on decreasing the AOB-related NH4 conversion rate, as autotrophic N2O formation is directly linked to AOB activity. The results showed that the biofilm system was more advantageous compared with suspended sludge systems. A higher AOB content resulted in a decrease in AOB activity, leading to fewer N2O emissions at the same reactor performance. The highest reduction in autotrophic N2O formation (SBR: 25%; Biofilm: 27%) was obtained by maximizing the aerated time per day and minimizing the number of aeration cycles (the suppression of nitrite-oxidizing bacteria still needed to be ensured). A higher biofilm thickness or a higher sludge mass in the SBR, however, did not have a noteworthy positive effect since no additional biomass could be kept in the system in the long term due to limited substrate availability. Besides nitritation, denitrification was also identified as a relevant source of N2O in both systems (biofilm: main source) due to the inhibition of N2O reduction by nitrous acid (elevated nitrite concentrations in combination with pH values < 7).

Green sludge dewatering and recycling technology for generating renewable energy and liquid nutrients: Bench- and pilot-scale studies

In this study, ultrasonication was performed under a low H2O2 dosage for dewatering and reducing activated sludge. Moreover, torrefaction was performed to convert the sludge remaining after ultrasonication into biochar, which is a renewable energy source. Factors including the H2O2 concentration, ultrasonication time and power, and torrefaction temperature and reaction time were systematically evaluated. The results of bench-scale tests indicated that high sludge volume and mass reductions (>50%) as well as high-carbohydrate and -protein content in the supernatant could be achieved through 20-s ultrasonication under a H2O2 dosage of 1.5% and ultrasonication power of 70-W. In these tests, the produced biochar exhibited a HHV of 12.8–14.4 MJ kg−1, a return of energy investment (ROEI) of 7.7–14.2, and 65.4% lower greenhouse gas (GHG) emissions upon combustion than did bituminous coal. In the pilot-scale tests, the produced biochar exhibited an ROEI of 10.4, and its GHG emissions on combustion were 74.8% lower than those of bituminous coal. The cost of the developed method is 84.6% lower than that of the conventional dewatering and disposal method. In summary, the proposed method is an energy-efficient, environment-friendly, and economically feasible method for producing biochar and recovering nutrients from supernatants without considerable GHG emissions.

Two-Dimensional Modelling of Sludge Heat and Mass Transfer in a Paddle Dryer

In this paper, we propose a concise but general two-dimensional model based on the penetration model in order to simulate the heat and mass transfer and drying kinetics of sludge in the paddle dryer. The sludge control equations were developed to simulate the heat and mass transfer of sludge and the penetration model was introduced to describe the mixing of sludge. Compared to the experimental results in the existing literature, the drying kinetics simulated simulated by the present model were in good agreement with the experimental data under various operation conditions. The effects of four key parameters on drying kinetics in the paddle dryer were studied. The results showed that the water content increased with the increase of sludge flowrate and the decrease of wall temperature and sludge density. Furthermore, the stirring velocity had little effect on the drying kinetics of the sludge. The present study contributes to the better understanding of the sludge drying kinetics and provides guidance for the optimal design of industrial paddle dryers.

The potential of microalgae Dunaliella salina to treat shrimp pond wastewater in a PAN/GO membrane bioreactor

Graphene has attracted a significant amount of attention because to its excellent mechanical, electrical, thermal, and optical characteristics. In this work, a membrane bioreactor with hollow fibre PAN/GO nanocomposite was studied for the treatment of Persian Gulf shrimp pond wastewater. Dunaliella salina microalgae have been used for better treatment and the formation of sludge mass in a shorter period of treatment in the MBR system. Additionally, GO nanoparticles were used in order to improve the hydrophilicity of the membranes. Various tests, such as Pure water permeate (PWP), X-ray diffraction spectroscopy (XRD), Atomic force microscopy (AFM), Dynamic light scattering (DLS), Contact angle (CA), Scanning electronic microscopy (SEM), Fourier transform infrared substances (FTIR) were used to characterize the synthesized membranes. To evaluate the treated wastewater, several factors were evaluated, including: TP, TN, TSS, NTU, BOD, COD, EC. The contact angle was reduced by the inclusion of GO nanoparticles from 53.8° for PAN-0 to 45.4° for PAN-3. The results of FTIR analysis confirmed the synthesis of GO and showed the formation of different deposits as fouling on the surface of the prepared membranes after MBR process. Also, the removal percentage of COD and BOD5 was over 90% for membranes with graphene oxide nanoparticles. The turbidity for all fabricated membranes were removed ∼98%. Also, very little fouling occurred in the membranes constructed with GO membranes and the maximum concentration of GO let to maximum performance regarding to the high potential of fouling control. In addition, the growth of Microalgae Dunaliella salina with shrimp wastewater was observed successfully. In conclusion, the finding of this work not only proposed a promising solution for controlling fouling in an MBR but also resulted in a benefit product, i.e. microalgae Dunaliella salina.

Effects of surface and mixed application of sewage sludge on Neolamarckia cadamba root growth

The utilization of sewage sludge in forests is an important way of recycling. However, the effect of sewage sludge application on woody plant root growth has been rarely reported. The effects of surface application and mixed application of sewage sludge (mass ratio in 10%) on the dynamics in root morphology of a fast-growing tree species (Neolamarckia cadamba), soil pH, electric conductivity, and heavy metal content of roots in different soil layers were analyzed by a rhizobox experiment. The relationship between root length and soil pH value, electric conducti-vity, and root heavy metal content were further analyzed. Results showed that mixed application of sewage sludge inhibited root length, root surface area, and root volume. After 120 and 240 days of mixed application, total root length in the 0-20 cm soil layer was 76.9% and 67.4% of that of no sewage sludge application, respectively. Surface application of sewage sludge did not affect root length and root surface area but increased root volume. The mixed application of sewage sludge significantly increased soil pH, electric conductivity, and root heavy metal content. Root Cd contents in 0-20 cm and 20-40 cm soil layers with the mixed application of sewage sludge were 11.5 and 10.0 times as that of no sewage sludge application, respectively. Soil electric conductivity had a significant nega-tive correlation with root length in 0-20 cm soil layer among different treatments. Root Cd content had a significant negative correlation with root length in both the surface and the mixed applications of sewage sludge. These results indicated that mixed application of sewage sludge could inhibit N. cadamba root growth mainly by increasing soil electric conductivity and root Cd content, while the surface application of sewage sludge did not affect root growth.