Dried Sewage Sludge Research Articles

Effectiveness of helminth egg reduction by solar drying and liming of sewage sludge.

The present study is aimed at assessing the effectiveness of solar drying process in terms of helminth egg reduction in sewage sludge (SS) generated from an activated sludge wastewater treatment plant (WWTP) in Marrakesh city (Morocco). It is also engaged to highlight a synergic effect of liming (1% CaO) and solar drying on helminth egg reduction. The solar drying process was conducted for 45days, in summer under a semi-arid climate in a pilot scale polycarbonate-based tunnel (2m3). Before undergoing solar drying process, data showed an important load of helminth eggs including Ascaris sp., Schistosoma spp., Capillaria spp., Trichuris spp., Ankylostome spp., Toxocara spp., and Taenia spp. in limed sludge (LS) and non-limed sludge (NLS) (15.2 and 17.9 eggs/g, respectively). Ascaris eggs were the most abundant (11.2 and 13.5 eggs/g in LS and NLS, respectively). By the end of the solar drying process, a considerable removal of the total helminth eggs was recorded in LS and NLS (92.8% and 91.6%, respectively). A complete removal of Schistosoma spp., Capillaria spp., Trichuris spp., Toxocara spp. and Taenia spp. was noted in LS and NLS. In the case of Ankylostome spp., data showed a total removal in LS and 81% in NLS; however, the final load is in agreement with the standards (0.4 egg/g). As for Ascaris spp., neither liming nor solar drying process allowed a complete removal (91% and 90% in NLS and LS, respectively) and the final load (1.1 egg/g) does not fulfill the WHO requirements for an agricultural use. Principal component analysis (PCA) demonstrated a negative correlation between dry matter (DM) content (hence temperature) and helminth egg concentration. No significant synergic effect of liming and solar drying process was showed by statistical analysis. This is substantiating that temperature is the key parameter involved in helminth egg removal while undergoing solar drying of SS.

Thermochemical Treatment of Sewage Sludge Ash (SSA)—Potential and Perspective in Poland

Phosphorus (P) recovery from sewage sludge ash (SSA) is one of the most promising approaches of phosphate rock substitution in mineral fertilizers and might be a sustainable way to secure supply of this raw material in the future. In the current investigation, the process of thermochemical treatment of SSA was applied to SSA coming from selected mono-incineration plants of municipal sewage sludge in Poland (Cracow, Gdansk, Gdynia, Lodz, Kielce and Szczecin). The Polish SSA was thermochemically converted in the presence of sodium (Na) additives and a reducing agent (dried sewage sludge) to obtain secondary raw materials for the production of marketable P fertilizers. The process had a positive impact on the bioavailability of phosphorus and reduced the content of heavy metals in the obtained products. The P solubility in neutral ammonium citrate, an indicator of its bioavailability, was significantly raised from 19.7–45.7% in the raw ashes and 76.5–100% in the thermochemically treated SSA. The content of nutrients in the recyclates was in the range of 15.7–19.2% P2O5, 10.8–14.2% CaO, 3.5–5.4% Na2O, 2.6–3.6% MgO and 0.9–1.3% K2O. The produced fertilizer raw materials meet the Polish norms for trace elements covered by the legislation: the content of lead was in the range 10.2–73.1 mg/kg, arsenic 4.8–22.7 mg/kg, cadmium 0.9–2.8 mg/kg and mercury <0.05 mg/kg. Thus, these products could be potentially directly used for fertilizer production. This work also includes an analysis of the possibilities of using ashes for fertilizer purposes in Poland, based on the assumptions indicated in the adopted strategic and planning documents regarding waste management and fertilizer production.

Evaluation and Emission Characterization of the Malodorous Substances Produced by Direct Drying of Sewage Sludge

Evaluation and Emission Characterization of the Malodorous Substances Produced by Direct Drying of Sewage Sludge

Loading Capacity of Sewage Sludge for Forestry Application in Chinese Provincial Capital Cities

The application of sewage sludge (SS) in forestry is considered a viable option. However, the long-term application of SS potentially leads to metal accumulation, posing an environmental risk. Understanding the loading capacity of SS for forestry application is therefore of great significance. We used data from published studies and statistical bulletins across 31 provincial capital cities (PCCs) in China to calculate the loading capacity (LC) of SS for forestry application for each PCC. The results are as follows: (1) the mean value of the priority control threshold was 33 t·ha−1·y−1 in 31 PCCs, while the variations ranged from 7 to 91 t·ha−1·y−1 among different PCCs. The priority control thresholds (Smins) of 1/2 PCCs were higher than 30 t·ha−1·y−1 (CJ-T 362-2011). The Smin values of Lanzhou, Tianjin, Hohhot, Shanghai, and Yinchuan were above 55 t·ha−1·y−1, but Smin values of Kunming and Changsha were below 10 t·ha−1·y−1. (2) Cd was the priority control metal in most of the PCCs (27/31), with the exception of Shanghai and Guangzhou (Cu), Beijing (Hg), and Tianjin (Zn). (3) The total loading capacity was 507 million t·y−1, which was 125 times higher than the total quantity of the dry SS (404 × 104 t) for the 31 PCCs. Our results have important practical significance for the use of urban sludge forest land in China and suggest that SS disposal policies need to be tailored to specific regions. We provide a scientific basis to guide the development of national and provincial forestry policies.

Comparison of dried sludge and sludge ash for phosphorus recovery with acidic and alkaline leaching

AbstractNowadays, the recovery of phosphorus has been in the spotlight due to its importance for food security and depleting sources. In this study, phosphorus recovery from dried sewage sludge and sludge ash by acid and alkaline leaching was evaluated. Optimum extraction time and temperature were determined as two hours and ambient temperature. Results showed the superiority of strong acidic conditions for leaching; 75 ml/g with 0.4N HCl and 25 ml/g with 0.6N HCl were determined as optimum conditions to achieve efficient phosphorus dissolution from sludge ash (94.6%) and dried sludge (91.1%), respectively, with the lower heavy metal concentrations. Lower L/S ratio put forward the dried sludge as a more advantageous resource for phosphorus extraction. Besides, by alkaline leaching of sludge ash and dried sludge, 60.3 and 70.3% phosphorus dissolutions were achieved with 75 ml/g and 1N NaOH; and the leachate was a suitable product for phosphorus precipitation due to its high pH.

Co-combustion of municipal dewatered sewage sludge and natural gas in an actual power plant

This study mainly aimed to determine the performance of the co-combustion of municipal dewatered sewage sludge and natural gas by using actual power plant data for the first time and adding it to published literature. Through a consideration of energy, a thermodynamic analysis of a power plant using municipal sewage sludge was carried out using actual plant data to assess its energetic performance. The fictive molecule C4·13H8·58O2N0·61S0.04 was obtained from the average chemical composition of the dry-based municipal sewage sludge. Energy losses in the plant and its units were determined. The net plant energy efficiencies were found to be 9.095%. The power plant produced 121 Wh of electricity per kg of municipal dewatered sewage sludge. The average value of CO2 emissions from electricity generation was found to be 888 g of CO2/kWhe. Power capacity of 1 MW can eliminate 72,406.7 tonnes of municipal dewatered sewage sludge annually. In an investigated city, 36.93 g of dry sewage sludge was produced per capita per day.

Energetic, environmental and economic analysis of drying municipal sewage sludge with a modified sustainable solar drying system

Disposal of sewage sludge is an important problem for the sustainability of cities. In recycling process of sewage sludge, a big part of energy demand is consumed in the drying process. Therefore, utilizing clean and sustainable energies in recycling process of sewage sludge can be a good solution. In this work, a drying chamber with transparent cover has been designed and analyzed in the process of drying sewage sludge experimentally and numerically. Also, a conventional drying chamber has been tested and its performance compared with modified drying chamber’s performance. The main purpose of modifying the drying chamber using transparent cover is to harvest more solar energy in the system and consequently reduction in the drying time. Moreover, in the drying tests a single-pass conventional unglazed solar air collector has been combined with the drying chamber. The performance tests of drying systems have been conducted in two various flow rates including 0.010 and 0.014 kg/s. Experimental and numerical findings demonstrated that using drying chamber with transparent cover reduced the drying time significantly. The obtained average specific energy consumption and specific moisture extraction rate values are in the range of 1.77–2.86 kWh/kg and 0.77–1.34 kg/kWh, respectively. Moreover, levelized cost of heating values were found between 1.7 and 2.0 $-ct/kWh for the system which uses drying chamber with transparent cover.

Oxygen consumption for the combustion of sewage sludge: a potential environmental parameter determined by an electrochemical YSZ oxygen sensor

ABSTRACT Oxygen consumption (OC) for the combustion of dried sewage sludge was determined by an equipped YSZ oxygen sensor. Probably due to the good combustion of the sludge, it was not affected by the temperature and oxygen concentration. However, it increased directly proportional to the rise of sludge amount. The mole ratio of OC/TOC agreed well with each entry and almost equalled 1, which indicated the feasibility of directly using OC to assess the organic burden in the wastes. As a result, OC in this study can be potentially applied to replace the chemical oxygen demand (COD) for the evaluation of samples involving solid-containing wastes (e.g., sewage sludge). Additionally, the easy determination of OC also promotes its advantage over COD because of the unavoidable drawbacks for the conventional COD determination.

Draining solar drying of sewage sludge: Experimental study and modeling

AbstractThe draining solar drying is considered as an innovative solution in the field of sanitation. The objective of this work is to investigate the feasibility and model the kinetics of the sludge solar drying in a lab‐scale draining greenhouse by varying the air flow rate during winter and summer. The first experiment was conducted without ventilation. Then, a series of experiences was carried out with increasing the air flow. The drying period varied between 3 and 6 days in summer and between 9 and 14 days in winter. By increasing the air velocity, the drying time decreased. For the drying rate curves, in summer, only the falling rate period existed. However, in winter, the curves did not follow any regular shape of drying kinetics. Nine mathematical equations existing in the literature were tested to identify the thin‐layer drying kinetics of sewage sludge inside the draining greenhouse. The Midilli‐Kucuk model was the most reliable for describing the evolution of reduced moisture content versus drying time in hot and cold periods. However, for different drying conditions, the Wang and Singh model was the least suitable. The results revealed also that the effective diffusivity increased when the air flow rate and the ambient temperature increased.

Influence of back-mixing on the convective drying of sewage sludge: The structural characteristics

Back-mixing is an operation that can be used to reinforce the texture of soft and pasty sludges to improve the drying effect. In this study, three mass fractions in a back-mixing operation (40%, 60%, and 70% on a dry basis) were chosen for convective sludge drying in a fixed bed. The structural characteristics including the total exchange surface, object volume, and shrinkage of the sludge bed were measured by X-ray macrotomography during the drying process. The average drying rates are 0.076 g/s (original sludge), 0.079 g/s (40% back-mixed sludge), 0.092 g/s (60% back-mixed sludge), and 0.099 g/s (70% back-mixed sludge), respectively. For the original sludge and three back-mixed sludges used, both the object volume and total exchange surface decrease in a quasi-linear manner with decreasing water content in the sludge. The final total exchange surface increases by 97.1% for the 70% back-mixed sludge compared with that of the original sludge. After drying, the shrinkage ratio of the object volume of the original sludge is 82.1%, however it is decreased to 50.8% when the 70% back-mixed sludge is used. The average convective mass transfer coefficient increases by 60% for the 70% back-mixed sludge compared with that of the original sludge. It was assumed for belt drying that, the lengths of the belt used for the 40% back-mixed sludge, 60% back-mixed sludge, and 70% back-mixed sludge will be nearly 0.96, 0.83, and 0.77 times, respectively, as long as that used for the original sludge.

Waste to Energy: Solid Fuel Production from Biogas Plant Digestate and Sewage Sludge by Torrefaction-Process Kinetics, Fuel Properties, and Energy Balance

Sustainable solutions are needed to manage increased energy demand and waste generation. Renewable energy production from abundant sewage sludge (SS) and digestate (D) from biogas is feasible. Concerns about feedstock contamination (heavy metals, pharmaceuticals, antibiotics, and antibiotic-resistant bacteria) in SS and D limits the use (e.g., agricultural) of these carbon-rich resources. Low temperature thermal conversion that results in carbonized solid fuel (CSF) has been proposed as sustainable waste utilization. The aim of the research was to investigate the feasibility of CSF production from SS and D via torrefaction. The CSF was produced at 200~300 °C (interval of 20 °C) for 20~60 min (interval 20 min). The torrefaction kinetics and CSF fuel properties were determined. Next, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of SS and D torrefaction were used to build models of energy demand for torrefaction. Finally, the evaluation of the energy balance of CSF production from SS and D was completed. The results showed that torrefaction improved the D-derived CSF’s higher heating value (HHV) up to 11% (p < 0.05), whereas no significant HHV changes for SS were observed. The torrefied D had the highest HHV of 20 MJ∙kg−1 under 300 °C and 30 min, (the curve fitted value from the measured time periods) compared to HHV = 18 MJ∙kg−1 for unprocessed D. The torrefied SS had the highest HHV = 14.8 MJ∙kg−1 under 200 °C and 20 min, compared to HHV 14.6 MJ∙kg−1 for raw SS. An unwanted result of the torrefaction was an increase in ash content in CSF, up to 40% and 22% for SS and D, respectively. The developed model showed that the torrefaction of dry SS and D could be energetically self-sufficient. Generating CSF with the highest HHV requires raw feedstock containing ~15.4 and 45.9 MJ∙kg−1 for SS and D, respectively (assuming that part of feedstock is a source of energy for the process). The results suggest that there is a potential to convert biogas D to CSF to provide renewable fuel for, e.g., plants currently fed/co-fed with municipal solid waste.

Evaluation of Suitability of Treated Sewage Sludge for Maize Cultivation

The worlds growing population demands more food and creates more waste. Economically viable and environmentally friendly would be to use sewage sludge for agricultural production. There are several limitations for this use – heavy metal content, pathogenic microorganisms, helminths etc.. The different methods of treatment of sewage sludge helps to overcome this problem. The aim of the study is to find the effects of treated sewage sludge on the growth of maize and changes in soil biological activity. Experiments were carried out with dry sewage sludge preparation (SSP) in the such combinations 1) SSP, 2) SSP+PK, 3) SSP+NPK. Controls- loamy soil without additional fertilizer, soil mixed with mineral fertilizer (Kristalon 18:18:18). Maize (Zea mays var. saccharata ‘Elan F1’) was grown. Experiments were arranged in 1L vegetation containers placed in open area with additional watering. Plant growth parameters and soil enzymatic activity was detected. The SSP alone and in combination with potassium and phosphorus fertilizers does not provide the maize with the mineral nutrients in appropriate value, therefore, the combination of SSP with nitrogen containing fertilizers significantly improves plant growth and promotes development. The use of SSP increases the microbiological activity of the soil. This can have a beneficial long-term effect on the mineral nutrition of plants.

Isothermal torrefaction kinetics for sewage sludge pretreatment

Torrefaction of sewage sludge, a by-product from waste water treatment plants, has been receiving increased attentions in terms of sustainable sludge treatment, energy recovery and possibility to mitigate the environmental impacts. Torrefied sewage sludge is recognized as a better solid fuel than the dry sewage sludge, and it is also beneficial for subsequent thermochemical processes. In this study, sewage sludge was subjected to different torrefaction conditions in a thermogravimetric analyzer. The thermogravimetric data were then simulated using a two-consecutive reaction model to reproduce the mass losses during torrefaction. The obtained results from the torrefaction of the non-lignocellulosic biomass are also compared with other lignocellulosic biomass including a softwood and a hardwood. The findings from this study reveal that the non-lignocellulosic biomass is less thermally resistant and degrades much faster than the lignocellulosic biomass during the first stage of torrefaction. Moreover, the solid yield from the sewage sludge torrefaction at temperatures less than 280 °C is lower than that from the woody biomass torrefaction. However, this trend is inverted when the torrefaction temperature attains 280 °C and higher. The results obtained are useful for new design or retrofit of the sewage sludge torrefaction processes.

Strength Performance of Sustainable Mortar Containing Recycle Sewage Sludge Ash (SSA)

Sewage sludge is a by-product generated within the wastewater treatment process. Severe concern arised as the sludge are massively been dumped to the landfill and it may affect the environment. Many studies had been conducted in reusing the sewage sludge as construction material, where it is one of the optional ways to solve the issue. In this study, dried sewage sludge was incinerated with two different temperatures in order to produce sewage sludge ash (SSA), which are 800°C and 1000°C. After few processes, this SSA then reused in mortar as cement replacement with the replacement percentage of 5%, 10%, 15% and 20% by weight. The strength performance of mortar specimens was investigated after 7, 28, 60 and 90 days of curing. From the results, it is clearly showed that the compressive strength of all mortar specimens increased when the period of curing was prolonged. Moreover, almost all compressive strength of SSA mortars was higher than the control mortar. Therefore, there is potential to reuse this waste material as part of construction materials and hence, its plays an important role for future researches in minimisation of waste.

Biochar and its impact on soil properties, growth and yield of okra plants

Applying biochar to the soil can mitigate problems that hinder agricultural production, such as water scarcity and low fertility soils. The objective of this research was to evaluate the impact of dry coconut husk biochar and sewage sludge combinations on soil chemical characteristics, growth, yield and water productivity of okra crop. The experiment was arranged in randomized blocks, with 6 treatments (CHB+BSS -coconut husk biochar + biochar of sewage sludge, CHB+RSS-coconut husk biochar + raw sewage sludge, BSS+RSS -biochar of sewage sludge + raw sewage sludge, CHB -coconut husk biochar, BSS -biochar of sewage sludge, WB -without biochar (control)). Plant height, number of fruits per plant, yield and water use productivity were evaluated. To evaluate the effect of biochar on soil, soil samples weretaken to determine pH, CEC, P, K, Ca, Mg concentrations after incorporation of biochar into the soil. The BSS + RSS and BSS treatments provided better results on okra production and growth characteristics with a 421.15% and 419% productivity increase, respectively, compared to the control treatment. The BSS and BSS + RSS treatments provided better water productivity,with values of 14.5 and 13.3kilogramproduced for each cubic meter of water applied, respectively.All soil chemical characteristics analyzed were modified when the biochar was incorporated into the soil. The results provide valuable insight that okra growers can embrace the use of the combination BSS+RSS and BSS, providing better yields and lower water use in growing this plant.

Effects of electromagnetic induction on migration and speciation of heavy metals in drying sewage sludge: Mechanistic insights

Novel and efficient drying method based on electromagnetic induction plate (EMI-P) heating was used to treat sewage sludge (SS). This work focused on the effects of EMI-P action on heavy metals (HMs) in dried SS. Surface functional groups, surface chemistry and microstructures of SS treated were investigated and compared to provide insights into the transformation mechanisms of HMs during EMI-P drying process. The results show that the EMI-P-dried SS showed undesirably total concentrations of Cd and Zn and leaching concentrations of HMs (Cr, Ni, Zn, Cd and As) exceeded the Chinese ground water standard (GB/T14848-2017). Ni, Zn, and As in the EMI-P-dried SS still exhibited high mobility, the leaching percent of Ni, Zn, and As (under 300 V and 500 V) can reach up to 28.56%/10.36%, 26.96%/26.61% and 30.64%/23.14%, respectively. Compared with conventional thermal drying, the EMI-P method can effectively reduce the eco-toxicity derived from HMs by 28.06% under 500 V condition. The stabilization effect of the EMI-P action can be attributed to the following: (1) EMI-P action promoted the generation of surface complexes with HMs, (2) HMs adsorption by silicate minerals was enhanced under high-frequency magnetic fields and (3) honeycomb structures of EMI-P dried SS with micropores provided abundant active sites to bond with HMs.

Agronomic evaluation of dried sewage sludge and sewage sludge ash as sources of nutrients for maize

Agronomic evaluation of dried sewage sludge and sewage sludge ash as sources of nutrients for maize

Sewage sludge pyrolysis coupled with self-supplied steam reforming for high quality syngas production and the influence of initial moisture content

A technology of sewage sludge (SS) pyrolysis coupled with self-supplied steam reforming of the volatile is developed to utilize the latent heat of the steam vapor released in the SS drying & pyrolysis process. An integrated reactor consisting of a vertical free-falling pyrolysis section and a horizontal screw-moved reforming section is designed for this purpose. The performance of the reactor shows that by changing the moving speed of the char in the reforming section, high quality syngas with an H2/CO ratio of 4.37 and a percentage of H2 + CO up to 66.58 vol% can be obtained at approximately 570–600 °C for the dry SS. There is an optimum moving speed of the screw for producing the highest volume of the syngas. A higher moving speed of the screw also results in a higher concentration of the aromatic compounds in the final pyrolysis oil. When the initial moisture content of SS increases from 0 to 65.50%, the H2/CO ratio and H2/CO2 ratio in the syngas increase from 4.37 to 30.87 and from 2.1 to 2.6 correspondingly, and the final oil yield decreases from 24.03 wt% to 14.16 wt%. Moreover, the total energy recovery efficiency decreases from 88.85% to 61.92%, while the energy portion of syngas shows a peak of 44.18% of the total energy input when the initial moisture content is 41.26%. The integrated reactor also provides a good opportunity for adding a catalyst such as dolomite to make the process more effective. The technology developed in this paper provides an approach to deal with SS with a relatively high moisture content.

Biofuel production from pyrolysis of waste cooking oil fried sludge in a fixed bed

Waste cooking oil was used to dry sewage sludge by fry-drying technology. The obtained oil-fried sludge, which contained waste cooking oil and sewage sludge, was converted into biofuel simultaneously via pyrolysis process in a fixed bed. The synergistic effects of sewage sludge and waste cooking oil on the pyrolysis products were also investigated. Comparing to pyrolysis of sludge, pyrolysis of oil-fried sludge can obtain 51.9% higher gas products, where H2 and CH4 yields were increased by 37.4% (up to 211 ml/g) and 163% (up to 155 ml/g), respectively. The lower heating value (LHV) of gas product from oil-fried sludge was 41.2% higher than that from sludge. The higher LHV of gaseous products can be beneficial to use for power generation and heating. This indicates that oil-fried sludge shows a potential feedstock can be converted into high valuable biofuel. Nevertheless, the experimental gas and tar yield values of oil-fried sludge were lower than calculated values, indicating that there is an anergy effect of interactions between SS and oil on gas and tar formations. This was because the oily materials layer inhibited the heat and mass transfer in the sludge pyrolysis process, and then hindering the conversion of sludge into gas and tar formation.

Screening of waste materials as adjuvants for drying sewage sludge based on environmental, technical and economic criteria

Thermal drying allows the reduction of the moisture contained in the sewage sludge (SS) formed in wastewater treatment plants (WWTP) to less than 80%. The management of the dried SS is easier and may have good properties as a soil amendment (carrying organic matter and N, P nutrients). This work aims to select the most appropriate drying adjuvant for application in full-scale and produce a material adequate for agriculture soil applications by applying two multi-criteria decision making (MCDM) methods, the MOORA and TOPSIS. The criteria weights were determined using the CRITIC method. Within the circular economy framework, four industrial wastes were considered as drying adjuvants: weathered coal fly ash (CFA), green liquor dregs (GLD), eggshell (ES), and rice husk (RH). Then, small cylinders of SS were extruded with 0.15 g adjuvant g−1 SSwb and dried at a constant temperature of 70 and 130 °C. Eleven criteria were grouped into three categories (environmental, technical, and economic). Both methods MOORA and TOPSIS showed that the use of GLD at 130 °C is the best option. Moreover, ES at 130 °C and GLD at 70 °C are also good options, and the choice should consider the need for removal of pathogenic contamination. The worst alternatives were CFA and RH at 70 °C according to both MCDM methods. The most influential criteria for decision making were the removal efficiency of pathogenic microorganisms, acid neutralization capacity (ANC) and germination index (GI).