Municipal Sewage Sludge Research Articles

Thermal Characterization, Kinetic Analysis and Co-Combustion of Sewage Sludge Coupled with High Ash Ekibastuz Coal

Efficient utilization of natural resources and possible valorization of solid waste materials such as sewage sludge into secondary materials via thermal conversion and simultaneously recovering energy is vital for sustainable development. The continuous increase in metropolises leads to an enormous production of wet sewage sludge, which creates major environmental and technical issues. In this paper, the samples of sewage sludge from Astana’s waste water treatment plant are analyzed for their thermochemical properties, followed by thermogravimetric and kinetic analysis using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. Overall, the calorific value of sewage sludge sample was 18.87 MJ/kg and was comparable to that of the bituminous coal samples. The activation energy varied from 140 to 410 kJ/mol with changing conversion from 0.1 to 0.7. Further, mono-combustion and co-combustion experiments of the sewage sludge with high ash bituminous coal were conducted using the laboratory scale bubbling fluidized bed rig, respectively. The difference in NOx emissions between mono-combustion of sewage sludge and co-combustion with coal were at around 150 ppm, while this value for SO2 was similar in average, but fluctuates between 150 and 350 ppm. Overall, the findings of this study will be useful in developing a co-combustion technology for a sustainable disposal of municipal sewage sludge.

Effects of Different Biochar and Effective Microorganism Agent Improvement Approaches on the Nutrient Release Characteristics and Potential of Compost

The nutrient release characteristics of four types of composts, pure municipal sewage sludge compost, corn straw biochar (CSB) improved compost, effective microorganism agent (EM) improved compost, and CSB+EM improved compost, in coastal wetland soil were examined through a soil incubation experiment. The effects of different composts on the spectral characteristics of soil dissolved organic matter (DOM) and microbial community were also investigated. The results demonstrated that the compost additions could significantly reduce soil pH, while increasing soil electrical conductivity and contents of plant available nutrients (e.g., dissolved organic carbon, NH4+-N, NO3--N, available phosphorus, and available potassium). By comparing the nutrient release potential among the improved composts, the CSB+EM-improved compost (CSB+EM-C) evidently had the highest nutrient release potential. Furthermore, the DOM in CSB+EM-C amended soil exhibited a higher humification degree than that of the other composts. The high-throughput sequencing results indicated that the compost additions increased the relative abundances of dominant bacteria at the phylum level, such as the Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. CSB+EM-C exhibited a greater potential to improve the relative abundance of these dominant bacteria phyla than other improved composts. Overall, among all the improvement approaches, the combined use of CSB and EM agent was the optimal composting strategy owing to its highest potentials of nutrient supply and soil quality improvement. The present findings can provide a solid scientific theoretical basis for establishing an effective technology strategy involving the combination of municipal sewage sludge utilization and degraded coastal wetland soil remediation.

Semi-continuous anaerobic co-digestion of thermal and thermal-alkali processed organic fraction of municipal solid waste: Methane yield, energy analysis, anaerobic microbiome

The semi-continuous anaerobic co-digestion (AcoD) of thermal and thermal-alkali pretreated organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) was studied under varying hydraulic retention times (HRT) and organic loading rates (OLR Three semi-continuous digesters were operated under control (non-pre-treated), thermally pretreated (125 °C), and thermal-alkali pretreated (125°C-3g/L NaOH) conditions at variable OLRs at 2.5, 4.0, 5.1, and 7.6 kgVS/m3.d and corresponding HRTs of 30, 20, 15, and 10 days. The 10 and 43% higher methane yield (0.445 m3/kgVS) and 11 and 57% higher VS removal (52%) was achieved for thermal-alkali pretreated digester at 5.1 kgVS/m3.d OLR over thermally pretreated (0.408 m3/kgVS, 45% VS removal) and control digesters (0.310 m3/kgVS, 33% VS removal), respectively. Thermal and thermal-alkali digesters failed on increasing the OLR to 7.6 kgVS/m3.d, whereas the control digester becomes upset at 5.1 kgVS/m3.d OLR. The metagenomic study revealed that Firmicutes, Bacteroidetes, Chloroflexi, Euryarchaeota, Proteobacteria, and Actinobacteria were the predominant bacterial population, whereas Methanosarcina and Methanothrix dominated the archaeal community. Energy balance analysis revealed that thermal alkali pretreatment showed the highest positive energy balance of 114.6 MJ/ton with an energy ratio of 1.25 compared with thermally pretreated (81.5 MJ/ton) and control samples (−46.9 MJ/ton). This work pave the way for scaleup of both thermal and thermal-alkali pre-treatment at 125 °C to realize the techno-economic and energy potential of the process.

AAC building components for modular construction using recycled materials

AbstractThe article presents the results of a study of the use of aggregates from the processing of wastewater treatment plant waste for the manufacture of large‐scale prefabricated building components means large‐scale autoclaved aerated concrete. This aggregate, applied to hydration‐bonded materials, makes it possible to obtain lightweight concretes (density 1400–1600 kg/m3) with increased thermal resistance. In addition, the addition of an aluminosilicate phase to the concrete mix can favorably affect mechanical characteristics and durability. The lightweight aggregate obtained using sewage sludge is characterized by high porosity, resulting from the complete combustion of the organic parts contained in the sludge (more than 90% d.m.), which act as a porophore in the ceramization process. This feature predestines this type of aggregate for use in hydration‐bonded materials that exhibit improved thermal insulation properties. The combination of sludge‐based lightweight aggregate technology with AAC production technology, therefore, implies a synergistic action to obtain a material with improved thermal insulation parameters combined with the mechanical strength expected for structural materials. An important environmental aspect of the proposed approach is the use of waste materials including municipal sewage sludge, which is particularly difficult to manage and dispose of, and the reduction of natural resource exploitation.

Hybrid Prediction-Driven High-Throughput Sustainability Screening for Advancing Waste-to-Dimethyl Ether Valorization.

Assessing the prospective climate preservation potential of novel, innovative, but immature chemical production techniques is limited by the high number of process synthesis options and the lack of reliable, high-throughput quantitative sustainability pre-screening methods. This study presents the sequential use of data-driven hybrid prediction (ANN-RSM-DOM) to streamline waste-to-dimethyl ether (DME) upcycling using a set of sustainability criteria. Artificial neural networks (ANNs) are developed to generate in silico waste valorization experimental results and ex-ante model the operating space of biorefineries applying the organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS). Aspen Plus process flowsheeting and ANN simulations are postprocessed using the response surface methodology (RSM) and desirability optimization method (DOM) to improve the in-depth mechanistic understanding of environmental systems and identify the most benign configurations. The hybrid prediction highlights the importance of targeted waste selection based on elemental composition and the need to design waste-specific DME synthesis to improve techno-economic and environmental performances. The developed framework reveals plant configurations with concurrent climate benefits (-1.241 and -2.128 kg CO2-eq (kg DME)-1) and low DME production costs (0.382 and 0.492 € (kg DME)-1) using OFMSW and SS feedstocks. Overall, the multi-scale explorative hybrid prediction facilitates early stage process synthesis, assists in the design of block units with nonlinear characteristics, resolves the simultaneous analysis of qualitative and quantitative variables, and enables the high-throughput sustainability screening of low technological readiness level processes.

Microplastic abundance and characterization in municipal sewage sludge from cities across upper Ganga River, India: Apprising microplastic uptakes and their toxicity in the plant during sludge application in agriculture

This study investigates the occurrence and characterization of microplastic (MP) in sewage sludge from 3 different cities along the Ganga River, India and their toxic impact while applying sludge for crop production. MP occurred in the ranges of 29.2–60.8 × 103 particles kg−1 with an abundance of 1–5 mm (11.12%), <1 mm–100 μm (32.65%), and 20–100 μm (56.23%) size particles. ATR-FTIR analysis suggested polypropylene, polyethylene, nylon, and polycarbonate as sludge's most common MP polymer. In lab scale trials, sludge MP showed significant toxicity in Vigna radiata and reduced vegetative growth and plant weight was recorded with sludge-inoculated setups. Seedlings with sludge exhibited higher activities of catalase, superoxide dismutase, hydrogen peroxide (H2O2), and malondialdehyde than the control setups. Furthermore, fluorescence microscopy confirmed the MP bioaccumulation in tested seedlings. In summary, our results suggested that wastewater treatment plants (WWTPs) sink large volumes of MP in sewage sludge, which could be hazardous while applying such biosolids for crop production. MP seasonal dynamics in local WWTPs and their role in the mobilization of other toxicant chemicals could be investigated in future studies in this series.

Anaerobic Co-digestion of sewage sludge and organic fraction of municipal solid waste: Focus on mix ratio optimization and synergistic effects

The utilization of municipal solid waste (MSW) and sewage sludge (SS) as a source of renewable energy is crucial in achieving sustainable and integrated MSW management. SS and organic fraction of municipal solid waste (OFMSW) can be anaerobically digested to produce methane for energy. However, anaerobic digestion of specific substrates is challenging with respect to substrate characteristics. The problem of mono-digestion can be mitigated by co-digestion of these two major organic wastes because of their complementary characteristics. Moreover, there is a lack of studies on optimization of different mix ratios of organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) based on total solids (TS). The study aims to optimize the mix ratio for anaerobic co-digestion of OFMSW and SS. The study further elucidates synergistic effects associated with the co-digestion process. Different mix ratios of SS and OFMSW (0:100, 20:80, 40:60, 60:40, 80:20, 100:0) at 5, 7.5 and 10% TS were assessed for biomethane potential assessment. The results showed that with an increase in SS in the mix ratio feed the methane yield increased by 91% and 50% as compared to mono digestion of sewage sludge and OFMSW respectively at TS 7.5%. Based on the kinetic analysis, it was observed that the lag phase reduced for 60:40 mix ratio leading to higher rate of biodegradation. Positive synergistic effects were observed for 40:60, 60:40 and 80:20 mix ratio of SS:OFMSW based on co-digestion impact factor value. Response surface modelling was used to get the optimized mix ratio and TS %. The optimum mix ratio with the highest methane yield (388 ml/gVS added) was 70:30 (SS: OFMSW) at TS 7.5% with a desirability value of 0.98. These findings demonstrate that co-digesting SS and OFMSW is a preferable alternative for harnessing renewable energy and managing organic waste in a sustainable manner.

Anaerobic mono and co-digestion of agro-industrial waste and municipal sewage sludge: Biogas production potential, kinetic modelling, and digestate characteristics

Lignocellulosic substrates, including wastes generated from agro-industrial activities, are bio-residues evaluated to put an end to the energy needs and sustainable waste disposal problems that the world is trying to deal with today. However, the slow rate of hydrolysis of such lignocellulosic wastes limits the biogas production efficiency with the mono-anaerobic digestion (AD) process. Therefore, anaerobic co-digestion (AnCoD) of such wastes with secondary raw materials rich in microorganisms and various nutrients, such as sewage sludge, is an economical and useful method for both enhancing biogas production and disposal of more waste. In this study, AD and AnCoD processes for biogas and methane production were investigated on okra waste (OW) and municipal sewage sludge (MSS) by using cattle manure as inoculation, which constitutes only 8% of the total working volume. Five different substrate mixing ratios (100%OW, 75%OW-25%MSS, 50%OW-50%MSS, 25%OW-75%MSS, and 100MSS%) were prepared to observe the effect of C/N ratio, maximum biogas production potential, methane content, and organic matter removal efficiency on AD and AnCoD processes. All bioreactors were operated in a batch process with 8% TS in mesophilic temperature for 25 days. The amount of biogas produced in the 100%OW experimental set for the AD process was 44% more than 100%MSS. However, the AnCoD process was more efficient than AD, and biogas and methane production increased by up to 66% and 112%, respectively, compared to the mono-substrate experimental set. The highest biogas production value was 1060 mL (375 mL/gVSremoved) with 60% methane content in the bioreactor consisting of 25%OW-75%MSS. As a result of AD and AnCoD process, soluble carbohydrate, protein and COD removal for all bioreactors were between 62% and 79%, 28%-68% and 54%-70%, respectively. The FT-IR peaks seen in digestates were consistent with the presence of functional groups formed as a result of AnCoD. Monod, Cone, Transference function, and Logistic function kinetic models were used for the estimation of cumulative biogas production efficiency. In addition, the energy potential of the methane produced as a result of the AD and AnCoD processes and the financial gain that can be obtained from its direct sale were evaluated.

Anaerobic Digestion of Municipal Sewage Sludge Integrated with Brewery Wastewater Treatment: Importance of Temperature and Mixing Ratio

Brewery wastewater is characterized by a high organic matter content and low pH, which may cause serious ecological hazards if it is discharged without any treatment. In this study, brewery wastewater treatment was integrated with anaerobic digestion of municipal sewage sludge. Additionally, the effects of temperature and mixing ratio of brewery wastewater were investigated. The results showed that the brewery wastewater mixing ratio (v/v) of 20% could maximize the biogas production during anaerobic digestion at the temperature of 34 °C. Additionally, regulating the appropriate mixing ratio, increasing operating temperature and adjusting pH were effective ways to enhance anaerobic digestion efficiency. Furthermore, the distribution of microbial communities was confirmed to be significantly influenced by the mixing ratio of brewery wastewater using high-throughput DNA sequencing technology. With the increasing mixing ratio of brewery wastewater, Firmicutes gradually dominated instead of Chloroflexi. Meanwhile, Methanolinea and Methanosarcina became the dominant methanogens, while the proportion of Methanothrix was significantly reduced. The results of this study will provide data to support the practical process operation of anaerobic co-digestion of brewery wastewater and municipal sewage sludge.

Quantitative Distribution and Contamination Risk Assessment of Cu and Zn in Municipal Sewage Sludge

One of the methods of managing sewage sludge (SS) is its soil application. This possibility is promoted by the chemical composition rich in organic matter and nutrients. However, heavy metal contents in SS must meet respective permissible limits. Among the heavy metals in SS, Cu and Zn are found in the largest amount; thus, this study focuses on these elements. The main aim of the study is to investigate the quantitative distribution of metals in sequentially separated fractions of sewage sludge. Additionally, the potential risk of environmental contamination with heavy metals was assessed in the case of SS application for agricultural purposes. The relevant analyses were conducted on four different examples of municipal SS. Based on the total amounts as well as those determined in the SS fractions, the following indices were calculated: Igeo (geoaccumulation index), ICF, (individual contamination factor), and RAC (risk assessment code). The use of data from the sequential analysis as well as the calculated indices made it possible to assess the usefulness of SS in practice in terms of potential introduction of Cu and Zn into the environment with the sludge dose. It was found that total Cu (Cutot) and Zn (Zntot) did not exceed the permissible limits binding within respective Polish and international regulations. Regardless of the years of study and the analyzed SS, Cutot ranged from 260.9 to 393.5 mg·kg−1, and Zntot from 475.5 to 1153.1 mg·kg−1. The amounts of Cu and Zn were predominantly reducible (bound to iron and manganese hydroxides, Fr. II) and oxidizable complexes (bound to organic matter and sulfides, Fr. III). The average amounts of Cu in Fr. II ranged from 149.4 to 172.4 mg·kg−1, while those of Zn in Fr. II ranged from 370.9 to 754.6 mg·kg−1. Cu amounts in Fr. III were from 160.9 to 183 mg·kg−1 and Zn amounts in Fr. III were from 104.9 to 171.9 mg·kg−1. Total content of metals as well as TOC values strongly determined the quantitative level of both elements in the SS fractions. Generally, with the increase in the total amount of metals, their levels in the sludge fractions increased. In turn, the increase in TOC resulted in a decrease in the amounts of Cu and Zn in the sludge fractions. Calculated Igeo and ICF ratios showed high and very high SS contamination with Cu and Zn. Igeo values for Cu, regardless of the year of study and sludge sample, that ranged from 4.62 to 5.43 and for Zn from 3.41 to 4.86. At the same time, the ICF values for Cu ranged from 8.59–23.04, and for Zn 15.42–44.47. The RAC values indicated a low (Cu) and medium (Zn) risk of using SS in terms of the potential metal availability in the environment. The RAC values ranged from 1.46 to 4.40% for Cu and from 9.63 to 23.13% for Zn.

Utilizing Sewage Sludge Slag, a By-Product of the Circulating Fluidized Bed Combustion Process, to Efficiently Remove Copper from Aquatic Environment

Currently, one of the greatest threats to the aquatic environment is industrial wastewater containing heavy metals and other toxic substances. Hence, it seems necessary to search for ecological and cheap technologies for removing metals from wastewater. In this research, slag was used as waste obtained in the circulating fluidized bed combustion technology (CFBC), which is considered to be a modern, clean, and very effective method of incineration of municipal sewage sludge. The physicochemical properties of the waste material were characterized using selected analytical techniques. Next, the processes of adsorption of Cu(II) ions on slag in aqueous solutions were investigated. The results showed a high metal removal efficiency of 98.8% at pH 1.8 and slag dosage 5 g/L. Numerous studies have demonstrated that high process efficiency at a level of at least 90% is attainable. Based on the Langmuir equation, the maximum adsorption capacity was calculated to be 70.3 mg/g. Kinetic analysis revealed that the process fits better into the pseudo-second-order reaction model and the Freundlich isotherm. The intraparticle diffusion model was considered as a rate-controlling step for Cu(II) adsorption. In summary, the slag waste produced in the CFBC technology seems to be a highly effective adsorbent for potential use in adsorption processes to remove heavy metals from the aquatic environment. This solution is in line with the current European ‘zero waste’ strategy and the assumptions of a sustainable development economy.

Geochemistry pollution status and ecotoxicological risk assessment of heavy metal(oid)s in soil influenced by co-landfilling of MSW and sewage sludge, Morocco

Landfilling activities are one of themajorsources of heavy metal(loid)s contamination. Thus, assessing the spatial distribution ofthese elementsand evaluatingtheirpotentialhazards to public health in the areas surrounding landfills is of utmost importance. In this paper, the synergistic effects of co-landfilling of Municipal Solid Waste (MSW) and Sewage Sludge (SS) were assessed using pollution indicators, PCA, HCA, and Montecarlo probabilistic human risk assessment. To do so, 19 soil, leachate, and sewage sludge samples were collected around the landfill and their content of heavy metal(oid)s was analyzed using Inductively Coupled Plasma (ICP-AES). The average concentrations of As, Cd, Cu, Pb, Zn, Cr, Ni, Co, and Fe were 0.98, 3.14, 36.87, 41.90, 148.43, 21.64, 32.07, 4.02, and 3143.74 mg/kg dry weight, respectively. The concentration of all metal(oid)s was higher than the geochemical background and the highest amount was observed at the first 100 m from the landfill and the sampling sites affected directly by sewage sludge. The values of pollution indexes (geo-accumulation index, enrichment factor, pollution load index, ecological risk index) showedthat soils in the vicinity of the landfill displayed moderate to high contamination level, with a strong potential ecological impact. Furthermore, multivariate statistical analysis demonstrated that anthropogenic sources related to disposal practices of MSW and SS are the main responsible behind the revealed pollution. In addition, the deterministic and probabilistic human risk assessment highlighted that the non-carcinogenic risk for children and adults still within the acceptable limits. However, carcinogenic risk was well above the threshold values (10−4) for children. The elevated pollution level reflected the dangerousness of synergistic dumping of SS and MSW, which renders the avoidance of their co-landfilling mandatory.

The Effects of Different Doses of Organic Waste on Prairie Cordgrass (Spartina Pectinata L.) Yield and Selected Energy Parameters

Increasingly cultivated all over the world, energy crops, with their large biomass production, can be used to produce liquid biofuel and biogas. The aim of the research was to evaluate the yield and selected energy parameters of prairie cordgrass (Spartina pectinata L.) treated with different doses of municipal sewage sludge and mushroom substrate. Heat of combustion, calorific values and ash content were investigated in the first three years of its cultivation. Carried out between 2018 and 2020, the research was based on a field experiment established at an experimental facility in Central-Eastern Poland. Organic waste doses, each of them introducing 170 kg N ha−1, were applied once in spring 2018 before planting pieces of Spartina pectinata rhizomes. The experimental factors (organic waste doses and years of research) significantly affected the yield of prairie cordgrass. Significantly, the highest yield of its biomass was produced in response to municipal sewage sludge applied together with mushroom substrate (O25 + PP75) and in response to mushroom substrate applied on its own (SMS). Those values, averaged over three years of research, were, respectively, 4.23 and 4.18 Mg ha−1. Organic waste treatment had a significant impact on ash content in dry matter. On average, the highest ash content in dry matter was recorded in response to mushroom substrate (5.73%) and the lowest (4.98%) in plants treated with the highest dose of sewage sludge together with the lowest dose of mushroom substrate (O75 + PP25). The higher dry matter content in plant biomass was, the better the energy parameters were.

Ocena możliwości rolniczego wykorzystania komunalnych osadów ściekowych

Ocena możliwości rolniczego wykorzystania komunalnych osadów ściekowych

Assessing the suitability of municipal sewage sludge and coconut bran as breeding medium for Oryza sativa L. seedlings and developing a standardized substrate

The utilization of organic solid waste (OSW) for preparing standardized seedling substrates is a main challenge due to its temporal and spatial variability. This study aims to form models based on data from the literature and validate them through experiments to explore a standardized seedling substrate. The typical OSW in Hainan Province, including municipal sewage sludge (MSS), coconut bran (CB), seaweed mud (SM), and municipal sewage sludge biochar (MSSB), was used as raw material. A series of six mixing ratios was tested, namely: T1 (0% MSS: 90% CB), T2 (10% MSS: 80% CB), T3 (30% MSS: 60% CB), T4 (50% MSS: 40% CB), T5 (70% MSS: 20% CB), and T6 (90% MSS: 0% CB). SM and MSSB were added as amendment materials at 5% (w/w) for each treatment. The physicochemical properties of substrates, agronomic traits of rice seedlings and microbial diversity were analyzed. The results showed that the four kinds of OSW played an active role in providing rich sources of nutrients. The dry weight of the above-ground part was 2.98 times greater in T3 than that of the commercial substrate. Furthermore, the microbial analysis showed a higher abundance of Actinobacteria in T3, representing the stability of the composted products. Finally, the successful fitting of the results with the linear regression models could establish relationship equations between the physicochemical properties of the substrate and the growth characteristics of seedlings. The relevant parameters suitable for the growth of rice seedlings were as follows: pH (6.46–7.01), EC (less than 2.12 mS cm−1), DD (0.13–0.16 g cm−3), and TPS (65.68–82.73%). This study proposed relevant parameters and models for standardization of seedling substrate, which would contribute to ensuring the quality of seedlings and OSW resource utilization.

Recycling reuse of municipal sewage sludge in sustainable structural materials: Preparation, properties, crystallization and microstructure analyses

As a common solid waste in daily life, the disposal of municipal sewage sludge has always been global hot issues concerned by the world environmentalists. The present study reported the fabrication of lightweight high-strength bricks as sustainable structural materials by using kaolin and recycled municipal sewage sludge waste, and systematically discussed the effect mechanism of sintering temperature on product technical properties from both phase composition and microstructure. It showed that after sintering at 1250–1400℃, the porosity, sintering shrinkage, bulk density, compressive and bending strength of lightweight high-strength bricks were 11.30–37.18%, 23.81–38.86%, 1.57–2.22 g/cm3, 35–105 MPa and 23–84 MPa, respectively. And the variation trend of sintering shrinkage, bulk density and mechanical strength was positively correlated with sintering temperature, but completely opposite to that of porosity. For the phase composition, the change of sintering temperature would not affect the crystallization phase types in bricks, which were all composed of aluminum iron phosphate (Al0.67Fe0.33PO4), cristobalite (tetragonal SiO2), hematite (Fe2O3), sillimanite (Al2O3·SiO2) and mullite (3Al2O3·2SiO2). For the microstructure, the melting and consolidation degrees of bricks were higher as the sintering temperature rose, and the structure became more dense and compact under the action of liquid glass phase, leading to a remarkable improvement and optimization of technical properties. Besides, the developed lightweight high-strength bricks presented strong competitiveness in structural materials, advancing a win–win for environment and development.

Nitrogen fixation of municipal sewage sludge by co-pyrolysis with biomass and KH2PO4-modified biochar addition

In order to reduce nitrogen emissions during municipal sewage sludge (MSS) pyrolysis, the effects of co-pyrolysis of MSS with biomass and the second adsorption of KH2PO4-modified biochar were investigated. It was found that co-pyrolysis with cellulose inhibited the conversion of nitrogen into pyrolytic gas, and increased the N content in pyrolytic biochar. And the nitrogen fixation rate increased with cellulose addition increasing. Besides, compared with different biomass, MSS co-pyrolysis with 30% sugarcane bagasse had the optimal effect on nitrogen fixation (39%). Moreover, KH2PO4-modified biochar addition increased the second adsorption of nitrogenous volatiles and fixed nitrogen into oxides-N. The total nitrogen fixation rate reached maximum (47.65%) at 5% KH2PO4 impregnation. Thus, it is an effective nitrogen fixation method that MSS co-pyrolysis of 30% sugarcane bagasse with the second absorption of 5% KH2PO4-modified biochar. This study provided an effective solution to improve the treatment of municipal sewage sludge by pyrolysis technology.

Preparation, characterization and nitrogen availability of nitrohumic acid as a slow-release nitrogen fertilizer

ABSTRACT Nitrohumic acids (NHAs) are considered as promising slow-release N fertilizers. In this study, NHA was produced from six organic feedstocks, including coal, leonardite, municipal waste compost, sewage sludge, and apple and beech biochars via nitration using nitric acid. The nitration process was conducted in two ways: (i) after humic acid (HA) extraction (NHAD), and (ii) before HA extraction (NHAID). The prepared NHAs were then characterized using FT-IR and CHNS analysis. Additionally, N mineralization of NHAs was investigated in a sandy loam soil sample. The FT-IR spectra showed that both methods of nitration loaded nitro (NO2) groups into the HA structure. However, the CHNS analysis indicated the highest rate of N increase for NHAD (106%) and NHAID (113%) extracted from leonardite. Moreover, on average, the total acidity and carboxylic groups of the HAs increased by 7.5% and 14.5% after the nitration processes, respectively. The highest extraction yields of NHAD (26.1%) and NHAID (42.1%) were also obtained from leonardite. Although the extraction yield of NHAID was on average two times higher than that of NHAD, NHAD indicated a higher soil N availability (1.4 times). We concluded that the NHAD extracted from leonardite could be considered as an alternative slow-release N fertilizer.

Experimental study on the formation characteristics of PM0.4 from preheating combustion of sewage sludge

Municipal sewage sludge (SS) is gaining increasing attention as a carbon–neutral fuel. Preheating combustion has been applied in coal combustion to reduce both PM0.4 and NOx. It is a promising technology for SS disposal while PM formation from preheating combustion of SS is still unknown. This study investigated the formation characteristics of PM0.4 from preheating combustion of SS. The effects of preheating temperature (Tp) and combustion temperature (Tc) on PM0.4 were analyzed. The experimental results showed that simultaneous reduction of PM0.4 and NOx from preheating combustion of SS can be achieved with Tp ≤ 1300 °C and Tc ≤ 1200 °C. The reduction of PM0.4 in preheating combustion compared to conventional combustion is mainly attributed to reduction in vaporization of Ca. Tc has more significant effect on PM0.4 while Tp can affect NOx more effectively. Because SS has a low content of fixed carbon, vaporization of refractory elements (Ca, Mg, Fe, Si and Al) through reduction reaction of refractory oxides mainly occurs under reductive atmosphere in preheating furnace. Increasing Tc will significantly increase vaporization of alkali metals (Na and K), S and Cl, while has no significant effect on vaporization of refractory elements. These are different with the results from high-alkali coal in our previous research (Reference [28]). Fe-precipitation agent used in waste water treatment results in uniform distribution of Fe in SS particles, which enhanced interaction between Fe and Si-Al containing minerals. This decreases reaction between Si-Al containing minerals and Na containing compounds. Therefore, even SS contains less Na and more Si-Al than high alkali coal, Na is easier to transfer to PM0.4 in preheating combustion of SS than high alkali coal.

Production of ethyl esters using municipal sewage sludge and porous ionic liquid coordinated with Burkholderia lipase

Lipase from Burkholderia species immobilized onto novel mesoporous polymeric ionic liquids (MO(Poly)Cn–BLE) could be utilized as a low–cost biocatalyst for the lipase-catalyzed synthesis of free fatty acid esters from dried municipal sewage sludge. To assess this, this investigation has focused on three main parts of this process: (i) the development of a series of large surface polymer synthesis; (ii) mesoporous polymeric biocatalyst preparation using lipase from Burkholderia sp. immobilization onto MO(Poly)Cn, and supports for this alongside Mesoporous polymer ionic liquid–1–bromooctane–lipase from Burkholderia sp. enzyme (MO(Poly)C18–BLE) were characterized using FT-IR, SEM, XPS, N2, and TGA; (iii) Response surface methodology was used to determine the optimal conditions for ester production from municipal sewage sludge lipids using a central composite design. Four process variables were assessed at three levels; a total of 13 experiments were performed to study the effects of the lipids: ethanol molar ratio, catalyst concentration, reaction time, and temperature on the ester’s yield. A 91.25% ester yield was obtained under optimal conditions: a 1:12 molar ratio of municipal sewage sludge lipid to ethanol, 225 wt% MO(Poly)C18–BLE, 5 h reaction time, 45 ℃ reaction temperature, and a constant 150 rpm agitation. This novel biocatalyst synthesis method and ester production process from municipal sewage sludge lipids may provide ecological and economic support for industrial biodiesel production in the future.