Treatment Of Municipal Sewage Sludge Research Articles

Properties of fly ash from thermal treatment of municipal sewage sludge in terms of EN 450-1

Properties of fly ash from thermal treatment of municipal sewage sludge in terms of EN 450-1

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.

Design of Urban Sludge Emission Reduction Optimisation Strategy Based on Fuzzy Neural Network

Abstract Urban sewage sludge treatment is important for sustainable utilisation and virtuous cycle of freshwater resources. However, with the improvement of sewage discharge standards, ensuring stable operation of sewage sludge treatment plants is becoming an urgent problem to be solved in the sewage treatment industry. This paper proposes a FNN control framework based on different working conditions to optimise the whole process of municipal sewage sludge treatment and discharge. The framework first divides the working conditions according to the weather, forming a separate feature and an input vector together with the typical indicators of other sewage treatment plants. Then the FNN is used to complete the control and optimisation of various indicators, achieving the dual objectives of reducing energy consumption and optimising water quality. Finally, the model is tested for the tracking index of sewage flow. The results demonstrate that the FNN control method used has significantly lower MAE than the single method in the two indexes of energy consumption and water quality evaluation. This provides new ideas for the optimisation of urban sewage sludge treatment process in the future. Overall, the paper effectively highlights the importance of urban sewage sludge treatment and presents a well-designed FNN control framework for optimising the treatment process. Additionally, the paper could benefit from further elaboration on the significance of the results obtained, and suggestions for future research in this area.

Production of Cationic Starch-Based Flocculants and Their Application in Thickening and Dewatering of the Municipal Sewage Sludge

Polymer flocculants are used to promote solid-liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes.

Neural Image Analysis for the Determination of Total and Volatile Solids in a Composted Sewage Sludge and Maize Straw Mixture

Waste management is one of most important challenges in environmental protection. Much effort is put into the development of waste treatment methods for further use. A serious problem is the treatment of municipal sewage sludge. One method that is useful for this substrate is composting. However, it is reasonable to compost a sewage sludge mixed with other substrates, such as maize straw. To carry out the composting process properly, it is necessary to control some parameters, including the total solids and volatile solids content in the composted mixture. In this paper, a method for the determination of the total solids and volatile solids content based on image analysis and neural networks was proposed. Image analysis was used for the determination of the colour and texture parameters. The three additional features describing the composted material were percentage of sewage sludge, type of maize straw, and stage of compost maturity. The neural models were developed based on various combinations of the input parameters. For both the total solids and volatile solids content, the most accurate models were obtained using all input parameters, including 30 parameters for image colour and texture and three features describing the composted material. The uncertainties of the developed models, expressed by the MAPE error, were 2.88% and 0.59%, respectively, for the prediction of the total solids and volatile solids content.

A novel dual circulating fluidized bed technology for thermal treatment of municipal sewage sludge with recovery of nutrients and energy

Sewage sludge (SS), a by-product of the wastewater treatment process, should be viewed not as waste, but as a potential resource for renewable energy and nutrient recovery. However, SS contains various toxic and harmful pollutants, e.g., pathogens, pharmaceutical residues, and microplastics. Through organic recycling and reuse of SS on land, these contaminants may leak into the environment, creating potential hazards to the ecosystem and human health. To tackle this issue, an advanced SS treatment technique within circular economy principles was proposed. In this process, mechanically dewatered SS with 20–25 % total solids is first dried at 110 °C in a circulating fluidized bed dryer and then combusted at 850 °C in a circulating fluidized bed reactor. Consequently, all the unwanted organic compounds are eliminated, and the ash – relatively high in nutrients and sufficiently low in heavy metals – can be further processed into fertilizers and used in forestry or farming. Moreover, the process is self-sufficient in terms of energy, enabling standalone operation without supplementary fuels, and providing excess heat that can be utilized, e.g., as district heat. This paper describes the process in detail and reviews experiences and lessons learned from the commissioning and trial operation of a newly erected 1.5 MWth sludge combustion plant with a throughput of 10 000 t/a. The operational performance of the plant has been verified based on continuous processing of dewatered SS, and the main operating parameters were consistent with design values. Therefore, the scale-up of this technique was considered both feasible and successful.

Techno-Economic Analysis of Scenarios on Energy and Phosphorus Recovery from Mono- and Co-Combustion of Municipal Sewage Sludge

This study evaluates the techno-economic feasibility of energy and phosphorus (P) fertilizer (PF) recovery from municipal sewage sludge (MSS) through incineration in new combustion plants. We evaluated the economic impact of five critical process design choices: (1) boiler type, (2) fuel (MSS mono-combustion/co-combustion with wheat straw), (3) production scale (10/100 MW), (4) products (heat, electricity, PF), and (5) ash destination. Aspen Plus modeling provided mass and energy balances of each technology scenario. The economic feasibility was evaluated by calculating the minimum selling price of the products, as well as the MSS gate fees required to reach profitability. The dependency on key boundary conditions (operating time, market prices, policy support) was also evaluated. The results showed a significant dependency on both energy and fertilizer market prices and on financial support in the form of an MSS gate fee. Heat was preferred over combined heat and power (CHP), which was feasible only on the largest scale (100 MW) at maximum annual operating time (8000 h/y). Co-combustion showed lower heat recovery cost (19–30 €/MWh) than mono-combustion (29–66 €/MWh) due to 25–35% lower energy demand and 17–25% higher fuel heating value. Co-combustion also showed promising performance for P recovery, as PF could be recovered without ash post-treatment and sold at a competitive price, and co-combustion could be applicable also in smaller cities. When implementing ash post-treatment, the final cost of ash-based PF was more than four times the price of commercial PF. In conclusion, investment in a new combustion plant for MSS treatment appears conditional to gate fees unless the boundary conditions would change significantly.

Ash fusion and mineral evolution during the co-firing of coal and municipal sewage sludge in power plants

By coupling the treatment of municipal sewage sludge (MSS) with large coal-fired units not only does it overcome the shortcomings of difficult combustion and the low calorific value of sludge, but it can also use the existing exhaust emission treatment devices of power plants to treat toxic gases and various pollutants discharged in the combustion process. It is a competent method for treating MSS, which has been more frequently used in coal-fired power plants in China in recent years. In this paper, raw coal, municipal sludge, fly ash and slag are sampled and analyzed from three full-scale power plants which are actually mixed with MSS. The melting characteristics and composition of ash obtained from raw coal and MSS at different mixing ratios and various temperatures are analyzed by ash fusion point determination meters, XRF and XRD, and the mineral evolution is simulated by Factsage. The results of the lab-scale study indicate that the ash melting characteristic temperature of MSS in three power plants is obviously lower than that of pulverized coal, and with an increase in the mixing ratio, the ash melting characteristic temperature of the mixed samples gradually decreases. The higher iron content in MSS is the main reason why the ash melting characteristic temperature of MSS and mixed samples is lower than that of coal, and hematite formed from the process is a common fluxing mineral. The analysis results for the slag and ash from three full-scale power plants co-firing MSS indicate that the main composition of slag and ash is mullite, and that co-firing MSS has little effect on the ash melting characteristics. The experimental results can provide reference for practical coal-fired power plants in reasonable mixing sludge, avoiding slagging and improving boiler efficiency.

Assessment of Ecotoxicity of Incinerated Sewage Sludge Ash (ISSA)

Combustion in fluidised bed boilers is one of the most commonly used methods of treatment of municipal sewage sludge. Fly ash (FA) and air pollution control (APC) residues are the solid by-products generated by flue gas treatment. There are significant differences in the chemical composition of these wastes. FA is composed of mainly SiO2, P2O5, CaO and metals such as Zn, Ti, Cu, Cr, Pb and Ni. APC residues mainly contain SO3 and Na2O. The leachability tests that were carried out indicate that these wastes display very low leachability of heavy metals (for example leachability of Pb was equal 0.0004 mg·dm−3 in both wastes, leachability of Cd was equal 0.0012 mg·dm−3 in FA an 0.00004 mg·dm−3 in APC). On the other hand, very high sulphate concentrations (49,375 mg·dm−3) were found in water extract for the APC residues. In order to determine the toxicity of these wastes for plants, pot experiments with different additions of waste to the soil were carried out (on Lepidium sativum and Sinapis alba). Tests based on seeds germinations (on Lepidium sativum) in water extracts from waste (in different concentrations) were also performed. The results obtained indicate the very high toxicity of APC residues. Complete inhibition of germination and growth of the test plants was found for all concentrations of the tested waste in water extract and for all additions of waste to the soil in pot experiments. Seed germination tests on water extracts from FA did not show any toxicity of this waste. Pot tests with FA showed their toxicity only with a high (30%) addition in soil.

Changes and release risk of typical pharmaceuticals and personal care products in sewage sludge during hydrothermal carbonization process

Hydrochars were obtained by hydrothermal carbonization treatment of municipal sewage sludge. Effects of reaction temperature (180–300 °C) and reaction time (2–15 h) on structural characteristics of the hydrochars, and changes and release risk of typical pharmaceuticals and personal care products (PPCPs) in the hydrochars were investigated. Reaction temperature played a more important role than reaction time on hydrochar properties and decarboxylation reaction was the primary process during the converting of sludge to hydrochars. The sludge hydrochars had higher yields, carbon recovery rates, polarity and less aromaticity than biochars. Hydrothermal process reduced PPCPs’ load in sludge hydrochars effectively except caffeine and acetaminophen. The hydrochars prepared at intermediate and high temperatures (240 and 300 °C) had higher caffeine concentrations than the original sludge, which can be ascribed to the transformation of N-containing precursors. The highest CaCl2 extracted caffeine concentration occurred at intermediate temperature of 240 °C (48.1 μg/kg) due to the stronger affinity of caffeine in the high-temperature hydrochars. Caffeine was not detected in hydroxypropyl-β-cyclodextrin (HPCD) extract. Hydrochars prepared at low temperature (180 °C) had a higher acetaminophen concentration than the original sludge, which was attributed to the high thermal stability temperature of acetaminophen. Low- and intermediate-temperature hydrochars had higher CaCl2 extracted acetaminophen concentrations. The HPCD extracted acetaminophen was low with a range of nd to 6.72 μg/kg. In conclusion, PPCPs are less likely to constitute a limiting factor on the farm application of sludge hydrochar. This study provides theoretical support for the safe application of sludge hydrochar in the farmland.

Influence of microwave-assisted pyrolysis parameters and additives on phosphorus speciation and transformation in phosphorus-enriched biochar derived from municipal sewage sludge

Municipal sewage sludge is rich in phosphorus, the conversion of which into phosphorus-enriched biochar via microwave-assisted pyrolysis (MWAP) can realize the efficient treatment of municipal sewage sludge and the recycling of phosphorus. This follows the concepts of the sustainable development of waste management and “cleaner production”. At present, fundamental knowledge is lacking on the use of MWAP to recover phosphorus from municipal sewage sludge. In this study, the effect of MWAP parameters (temperature, power, and residence time) and additives on the properties of phosphorus-enriched biochar and the migration and transformation of phosphorus were investigated. The pH, surface area, and total phosphorous increased with increasing temperature and power, whereas a greater residence time promoted the conversion of non-apatite inorganic phosphorus (NAIP) into apatite inorganic phosphorous (AP). CaO addition promoted the conversion of NAIP into AP, whereas MgCl2 promoted the conversion of AP into NAIP. The simultaneous addition of CaO and MgCl2 led to antagonism, with CaO being dominant, demonstrating that the original phosphorus components prefer to combine with CaO. Phosphorus recovery was optimal at temperatures 500–600 °C and a residence time of 150 min. The addition of 9% CaO or 6% CaO +6% MgCl2 was sufficient to convert sewage sludge into phosphorus into AP. Under such conditions, AP contents in phosphorus-enriched biochar increased 1.4 times compared to that of additive-free biochar. Our study highlights the potential of MWAP for closing the phosphorus cycle and for producing fertilizers from complex materials, such as municipal sewage sludge.

Municipal sewage sludge energetic conversion as a tool for environmental sustainability: production of innovative biofuels and biochar.

In this study, municipal sewage sludge (MSS) is converted simultaneously into renewable biofuels (bio-oil, syngas) and high value-added products (biochar) using a fixed bed pyrolyzer. This work examines the combined effect of two factors: final pyrolysis temperature (°C) and MSS moisture content (%) on pyrogenic product yields and characteristics. A centered composite experimental design (CCD) is established for pyrolysis process optimization by adopting the response surface methodology (RSM). The statistical results indicate that the optimal conditions considering all studied factors and responses are 550 °C as final pyrolysis temperature and 15% as MSS moisture content. In these optimal conditions, biofuels yield is around 48 wt%, whereas biochar yield is about 52 wt%. The pyrolysis products characterizations reveal that (i) pyrolytic oil has a complex molecular composition rich with n-alkanes, n-alkenes, carboxylic acids, and aromatic compounds; (ii) bio-oil presents a high-energy content (high heating value HHV around 30.6 MJ/kg); (iii) syngas mixture has a good calorific value (HHV up to 8 MJ/kg), which could be used as renewable energy vector or for pyrolysis reactor heating; and (iv) biochar residue has good aliphatic and oxygenated group contents favoring its application as biofertilizer. These findings suggest that MSS conversion into biofuels and biochar is an appropriate approach for MSS treatment. MSS-to-energy could be proposed as an element for circular economy concept due to its effectiveness in producing high value-added and sustainable products and reducing environmental problems linked to MSS disposal.

Effect of Mussel Shells as a Permeable Reactive Barrier in Municipal Sewage Sludge Treatment by Electrokinetic Remediation

IIn this work, it was evaluate the utilization of mussel shells (raw and calcinated) as a permeable reactive barrier (PRB) for the treatment of municipal sewage sludge (MSS) contaminated with heavy metals, creating a novel combined system, which integrates two technologies: electrokinetic remediation technology, and adsorption by the utilization of mussel shells adsorbents. Regarding the adsorption process into the mussel shells adsorbents, it was also aimed to study the influence of aragonite and calcite on the adsorption of lead (Pb), copper (Cu), chromium (Cr), and zinc (Zn). For the preparation of the PRB, it was used three adsorbents: MEXMT (raw mussel shells); MEXMT 600 (mussel shells calcinated at 600°C) and finally, a commercial calcium carbonate (CCCom). It was applied an electric current of 1 V cm-1 and it was used an adsorbent/sludge ratio of 30 g kg-1 of contaminated sludge for the preparation of the PRB. Results proved that this process is perfectly suited for the removal of the heavy metals understudy from the sludge, especially with MEXMT (raw mussel shells) adsorbent. With this adsorbent, at the end of the 92 hours of operation time, it was obtained high removal rates for each metal in study. Results demonstrate that higher removals rates were achieved in lead (92%), followed by zinc (82%), copper (76%), and finally chromium with 72%. Based on these results, it was proved the technical viability of the proposed technology (electrokinetic remediation with raw mussel shells as a permeable reactive barrier) to treat municipal sewage sludges.

Sewage sludge ditch for recovering heavy metals can improve crop yield and soil environmental quality

The treatment and disposal of municipal sewage sludge (MSS) is an urgent problem to be resolved in many countries. Safely using the nutrients within MSS to increase crop yield and enhance the fertility of poor soil could contribute to achieving sustainable development. An indirect use of MSS in ditches alongside Pennisetum hybridum plants was studied in field plots for 30 months and the contents of heavy metals and macronutrients were monitored in soil, sludge and plant samples. We found that the yield of P. hybridum was significantly increased by 2.39 to 2.80 times and the treated plants had higher N content compared with no sludge. In addition, the organic matter (OM) and N contents in the planted soil increased significantly compared with the initial soil. The OM content in the planted soil of the MSS treatment was 2.9 to 5.2 times higher than that with no sludge, and N increased by 2.0 to 3.8 times. However, MSS had no significant effect on the N, P and K contents in the soil at the bottom of the MSS ditch, and the content of heavy metals (Cd, Pb, Cu and Zn) were also within the safe range. Moreover, the moisture content and phytotoxicity of MSS after this indirect use were reduced and the heavy metal contents changed little, which is favorable to the further disposal of recovered MSS. Therefore, this indirect use of MSS is beneficial to agricultural production, soil quality and environmental sustainability.

Microwave treatment of municipal sewage sludge: Evaluation of the drying performance and energy demand of a pilot-scale microwave drying system

Sewage sludge management and treatment can represent up to approximately 30% of the overall operational costs of a wastewater treatment plant. Microwave (MW) drying has been recognized as a feasible technology for sludge treatment. However, MW drying systems exhibit high energy expenditures due to: (i) unnecessary heating of the cavity and other components of the system, (ii) ineffective extraction of the condensate from the irradiation cavity, and (iii) an inefficient use of the microwave energy, among others issues. This study investigated the performance of a novel pilot-scale MW system for sludge drying, specifically designed addressing the shortcomings previously described. The performance of the system was assessed drying municipal centrifuged wasted activated sludge at MW output powers from 1 to 6 kW and evaluating the system's drying rates and exposure times, specific energy outputs, MW generation efficiencies, overall energy efficiencies, and specific energy consumption. The results indicated that MW drying significantly extends the duration of the constant rate drying period associated with the evaporation of the unbound sludge water, a phase associated with low energy input requirement for evaporating water. Moreover, the higher the MW output power, the higher the sludge power absorption density, and the MW generation efficiency. MW generation efficiencies of up to 70% were reported. The higher the power absorption density, the lower the chances for energy losses in the form of reflected power and/or energy dissipated into the MW system. Specific energy consumptions as low as 2.6 MJ L−1 (0.74 kWh L−1) could be achieved, well in the range of conventional thermal dryers. The results obtained in this research provide sufficient evidence to conclude that the modifications introduced to the novel pilot-scale MW system mitigated the shortcomings of existing MW systems, and that the technology has great potential to effectively and efficiently drying municipal sewage sludge.

Application of ash and municipal sewage sludge as macronutrient sources in sustainable plant biomass production

Owing to the growing volumes of ash and sewage sludge waste, there is a requirement for theoretical and practical research into the use of these wastes as a source of nutrients. However, there are relatively few studies on the transfer of macronutrients in soil-plant systems amended with ash-sewage sludge mixtures under field conditions. The aim of the study was to determine the effect of bituminous coal ash (AC), biomass ash (AB), and municipal sewage sludge (MSS) on the quantity and quality of a grass-legume mixture. During a 6 year field experiment on a sandy loam soil treated with the wastes, applied as mixtures or separately, the plant yield; N, P, K, Na, Mg, and Ca uptake by plants; macronutrient content and ratios in the plant biomass; and the recovery rate of macronutrients by plants were evaluated. The AB-MSS treatment increased the yield in comparison to that where the wastes were applied separately. The N, P, and Ca contents in the plant biomass and N and P uptake under ash-sludge treatments were in the range observed for the ash and sewage sludge. The AB-MSS co-application resulted in the highest K uptake. The AC-MSS treatment increased K and Mg uptake in relation to AC treatment. When AC or AB was added to the MSS, the Ca uptake increased relative to the MSS treatment. The plant biomass under the AB treatment was optimal for biofuel purposes in terms of the chemical composition. The co-application of AC or AB with MSS resulted in the optimum Ca:Mg ratio for fodder purposes. The recovery rate of the macroelements decreased in the following order: K, N, P, Mg, Na, and Ca. The results support the co-application of solid wastes such as ash and municipal sewage sludge to improve productivity, support the recycling of macronutrients, improve sustainability through the reduction of ash and sewage sludge disposal, and reduce reliance on mineral fertilizer.

Enviromental aspect of using ash from thermal treatment of municipal sewage sludge in hardening slurries

Enviromental aspect of using ash from thermal treatment of municipal sewage sludge in hardening slurries

The Effect of Hydrolysis on Properties of Soot and Tar During the Pyrolysis of Sewage Sludge

In this study, we evaluate the effect of hydrolysis treatment on the properties of tar and soot produced during the pyrolysis of sewage sludge at different operating temperatures (500–800 °C). The pyrolysis experiments were performed in a two-stage tubular fixed-bed reactor at atmospheric pressure. Raw sludge and hydrolysis-treated sludge (at pressure of 0.4 MPa and temperature 200 °C) samples were collected from local municipal sewage sludge treatment plant. The tar and soot samples obtained from pyrolysis at different temperatures were characterized by gas chromatography–mass spectrometry and scanning electron microscopy with energy dispersive X-ray spectroscopy, respectively. The results showed that increase in the pyrolysis temperature decreases the tar and soot yield for both raw and hydrolysis-treated sludge. The minimum tar yield was achieved with hydrolysis-treated sludge at 800 °C. The soot from raw sludge pyrolysis was of greater yield at high temperature than hydrolysis-treated sludge pyrolysis. The tar from pyrolysis of hydrolysis-treated sludge had more aliphatic character as compared to raw sewage sludge. The formation of heavy polycyclic aromatic hydrocarbons during pyrolysis of hydrolysis-treated sludge was lower at high temperatures than that of raw sludge. The aromatic hydrocarbons yield of hydrolysis-treated sludge was higher as compared to raw sludge at 800 °C.

Orthogonal experimental study on hydrothermal treatment of municipal sewage sludge for mechanical dewatering followed by thermal drying

This work is aimed at demonstrating the effect of hydrothermal treatment on the mechanical dewatering, thermal drying and stickiness of sewage sludge from two different wastewater treatment plants (SS1 and SS2). The analysis of particle size, microstructure and volatile matter content of sludge was conducted to explore the influencing mechanism of hydrothermal treatment. The impact and significance of three factors, i.e. hydrothermal temperature (130–220 °C), retention time (30–75 min) and calcium oxide content (0–5 wt.%), were studied by an orthogonal method. Range and variable analysis were carried out to investigate the significance of the factors. The results indicated that sludge particle size showed a 10–25% reduction after hydrothermal treatment, indicating a degradation of EPS and bacterial cells, which was also confirmed by microstructural analysis. Sludge dewatering performance was markedly promoted by increasing hydrothermal temperature, intention time or CaO content. But CaO showed 1.8–7.8 times higher significance than that of hydrothermal temperature and intention time. On the other hand, both hydrothermal temperature and retention time showed 2–5 times higher significance on chemical oxygen demand of filtrate and drying rate of dewatered sludge cakes than that of CaO. Increasing hydrothermal temperature or retention time led to the increase of the chemical oxygen demand and the decrease of the drying rate in general. Sludge decomposition was also manifested by the change of its volatile matter content which showed a strong positive correlation with the water content of dewatered sludge cakes and a negative correlation with the adhesive and cohesive stress of dewatered sludge cakes. Finally, the economic efficiency of hydrothermal treated sludge dewatering and thermal drying system was calculated and compared with that of conventional direct thermal drying. The total energy consumption of the system is about 25–40% lower than conventional drying for both of sludge, and the operation cost of the system is about 17–30% lower than that of the conventional drying.

Papermaking potential of Pennisetum hybridum fiber after fertilizing treatment with municipal sewage sludge

This study uses municipal sewage sludge (MSS) as a fertilizer for cultivating Pennisetum hybridum (hybrid Giant Napier grass). The effects of the MSS treatment on the chemical composition of Pennisetum hybridum and on the properties of paper made from its pulp were investigated. The study found that the holocellulose content of Pennisetum hybridum exceeded 72% and the fiber length reached 0.83 mm for one-year-old MSS treated plants. The tensile index of paper made from Napier grass fiber increased by 194% after beating. SEM observation revealed that the Pennisetum hybridum fiber bonded more tightly after beating. The content of carboxylic acid groups was similar in the fibers of 3-month-old and 1-year-old hybrid Giant Napier plants, and higher than that for 1.5-year-old plants. The present research demonstrates that Pennisetum hybridum fiber is suitable for pulping and paper-making after fertilizing treatment of the plants with MSS, which provides new ways for MSS utilization.