Sludge Ratio Research Articles

Conversion of palm oil sludge to biodiesel using sulphuric acid as catalyst

The present study focuses on utilizing palm oil sludge (POS) as low-cost feed stock for biodiesel production. The esterification reaction was performed by varying sulphuric acid dosage (2–5% wt), methanol to palm oil sludge molar ratio (3.5:1–9.5:1), reaction time (30–120 min), temperature 60 C and stirred speed 400 rpm. The free fatty acids (FFA) considerably reduced from 17.76% to 1.34% and maximum esters yield was observed to be 91.56% at optimal conditions, 4 wt % H2SO4, methanol to palm oil sludge ratio 7.5:1 and 60 min. The biodiesel was produced by transesterification process by varying sodium hydroxide catalyst concentration from 0.25 to 1.5 wt%. The maximum biodiesel yield of 92.2% was obtained at 0.25 wt% of NaOH. The biodiesel was tested for the fuel properties as per the IS 1448 protocol and compared with normal diesel fuel with reference to ASTM D6751 standards.

Bio-Enhanced Degradation Strategies for Fluoroquinolones in the Sewage Sludge Composting Stage: Molecular Modification and Resistance Gene Regulation.

The molecular/protein–protein docking and the index normalization method assisted by the entropy weight method were used to quantitatively evaluate the biodegradability of fluoroquinolones (FQs) under different biodegradation systems. Four biodegradability three-dimensional quantitative structure–activity relationship (3D-QSAR) models of FQs were constructed to design FQ derivatives with improved biodegradability. Through the evaluation of the environmental friendliness and functional properties, the FQ derivatives with high biodegradability, improved functionality, and environmental friendliness were screened. Moreover, four bio-enhanced degradation scenarios of FQs were set up according to the different temperatures and carbon–nitrogen ratio (C/N) in the sewage sludge composting stage, and the molecular dynamic (MD) simulation assisted by protein–protein docking was used to screen the external environmental factors that promote the degradation of FQs by thermophilic bacteria or group under different scenarios. Finally, MD simulation assisted by sampling method was used to validate and screen the application scheme of field measures to enhance the expression of antibacterial resistance of FQ derivatives in an agricultural soil environment after activated sludge land use. This study aims to provide theoretical support for the development of highly biodegradable FQ derivatives and the mitigation of potential risks that FQs may pose to the environment and humans through the food chain.

Higher helminth ova counts and incomplete decomposition in sand-enveloped latrine pits in a coastal sub-district of Bangladesh.

Pit latrines are the most common latrine technology in rural Bangladesh, and untreated effluent from pits can directly contaminate surrounding aquifers. Sand barriers installed around the latrine pit can help reduce contamination but can also alter the decomposition of the fecal sludge and accelerate pit fill-up, which can counteract their benefits. We aimed to evaluate whether there was a difference in decomposition of fecal sludge and survival of soil-transmitted helminth (STH) ova among latrines where a 50-cm sand barrier was installed surrounding and at the bottom of the pit, compared to latrines without a sand barrier, in coastal Bangladesh. We assessed decomposition in latrine pits by measuring the carbon-nitrogen (C/N) ratio of fecal sludge. We enumerated Ascaris lumbricoides and Trichuris trichiura ova in the pit following 18 and 24 months of latrine use. We compared these outcomes between latrines with and without sand barriers using generalized linear models with robust standard errors to adjust for clustering at the village level. The C/N ratio in latrines with and without a sand barrier was 13.47 vs. 22.64 (mean difference: 9.16, 95% CI: 0.15, 18.18). Pits with sand barriers filled more quickly and were reportedly emptied three times more frequently than pits without; 27/34 latrines with sand barriers vs. 9/34 latrines without barriers were emptied in the previous six months. Most reported disposal methods were unsafe. Compared to latrines without sand barriers, latrines with sand barriers had significantly higher log10 mean counts of non-larvated A. lumbricoides ova (log10 mean difference: 0.35, 95% CI: 0.12, 0.58) and T. trichiura ova (log10 mean difference: 0.47, 95% CI: 0.20, 0.73). Larvated ova counts were similar for the two types of latrines for both A. lumbricoides and T. trichiura. Our findings suggest that sand barriers help contain helminth ova within the pits but pits with barriers fill up more quickly, leading to more frequent emptying of insufficiently decomposed fecal sludge. Further research is required on latrine technologies that can both isolate pathogens from the environment and achieve rapid decomposition.

Anaerobic codigestion of excess sludge with chicken manure with a focus on methane yield and digestate dewaterability

The effects of the mixing ratio of excess sludge (ES) with chicken manure (CM) on methane yield and digestate dewaterability were investigated at thermophilic and mesophilic temperatures. Batch experiments were performed at five different volatile solid ratios (ES/CM). Compared with anaerobic digestion of ES alone, codigestion of ES with CM increased methane yield 82.4–123.1 mL g−1-VSadded (mesophilic) and 33.9–171.3 mL g−1-VSadded (thermophilic), respectively. The normalized capillary suction time (NCST) and TS of thickened digestate (3.09–8.29 s g−1-TS, 17.51 %–18.83 %) at mesophilic temperatures were superior to these (6.81–10.14 s g−1-TS, 16.66 %–18.30 %) at thermophilic temperatures. But the gap decreased with increasing CM proportion in the substrate. The results indicated that anaerobic codigestion of ES and CM at a proper mixing ratio (ES/CM = 1:1.5–2) could obtain a high methane yield and an adequate digestate dewaterability.

Handling the Sludge When Using Polyaluminum Chloride as a Coagulant in the Potable Water Treatment Process

The sludge produced in the treatment process depends on the type of coagulant and other chemicals used and the suspended particles present in raw water. Discarding this sludge in the landfills poses pollution of both ground and surface water, disturbing the lives in the water and the water quality. The primary potable water provider in Sri Lanka is the National Water Supply and Drainage Board. It focuses on finding ways of disposal, sustainable practices, and possible applications of the water treatment sludge. This research aims to identify the aluminum level in the potable water treatment sludge of the Konduwattuvana water treatment plant in Ampara and to utilize that sludge as an alternative raw material in burnt clay brick manufacturing. The national standards and limitations of the sludge content and the standard brick manufacturing process were followed. To reach the aim, a sequence of tests was conducted, and the brick characteristics are subjected to test for different sludge ratios according to the Sri Lankan Standard of 36:1978 for burnt clay bricks. Experimental results show that the aluminum content in liquid sludge and sludge cake was found to be 231.6 mg.L-1 and 54.9 mg.L-1, respectively, which implies that the sludge contains aluminum. The optimum sludge ratio to produce burnt clay bricks was found to be 10% of the total weight of the brick.

A pilot-scale study of electrocoagulation on phosphorus removal from animal manure and the economic analysis

Manure management is a challenge as the animal barns are tend to be larger operations. Electrocoagulation has a great potential to be applied in animal barns because it can effectively separate liquid and solid as well as nitrogen and phosphorus from animal manure. This work evaluated a pilot scale electrocoagulation with low carbon steel as electrodes working on dairy manure, shallow-pit and deep-pit swine manure. Over 66% of the phosphorus in electrocoagulation treated swine manure was recovered in sludge with less than 10% of the phosphorus in the untreated volume. The TN/P2O5 ratio in swine manure sludge after electrocoagulation decreased to 0.52–0.78 while it increased to 10.61–38.56 in the supernatant after electrocoagulation, which significantly reduced the risk of phosphorus overdose as manure fertiliser to pollute the environment. However, the pilot electrocoagulation removed 79.3% of the dairy manure phosphorus into sludge while the sludge volume was 48% of the total volume. The economic analysis showed that an electrocoagulation system in a barn with 2400 head grown-finish pigs for 20 years would add $1.04 and $3.32 per pig of additional annualised cost in a shallow-pit swine barn and deep-pit swine barn, respectively. The environmental benefits of manure nutrient balancing and phosphorus sustainability make it worth to develop electrocoagulation technology on animal barns.

The Mandatory 4 Years Desludging Frequency of Underground Septic Tanks in Residential Areas: A Case Study in Sibu Sarawak, East Malaysia

Underground septic tanks are the most common and conventional primary black water treatment adopted by local households in Sarawak. To ensure its usefulness, periodic mandatory desludging or emptying of the various types of rateable holdings was enforced from 1998. The current mandatory desludging frequency is 4 years for residential households, although its effectiveness is still not clear, substantial annual finance and subsidies are being allocated by the Sarawak State Government. In this study, the underground septic tanks in Sibu located in residential areas in Sarawak, East Malaysia, were evaluated quantitatively based on the measured faecal sludge with a known retention time in respect to the regulated desludging frequency. Furthermore, various problems were encountered during the initial measurement carried out by sludge judge which typically used by the wastewater treatment and chemical plants. A modified PVC pipe was proposed to overcome these observed problems. This has greatly improved the measurement time and substantially reduced unwanted impediments for the contractor during desludging. The back analysis results showed that the recommended desludging frequency based on the ratio of total sludge and scum to the effective working volume in 30% and 50% thresholds for residential areas were 3.82 and 6.36 years, respectively. Furthermore, it was discovered that there was a potential to adjust the existing mandatory 4 years desludging frequency to a longer period for cost-effective consideration. This study is strictly on the physical quantity measurement of sludge and scum volumes for the known retention times. The complex influences of microbiological activities, micro-environmental factors and sizes or geometries of septic tanks for faecal sludge production were not considered.

Impacts of food waste to sludge ratios on microbial dynamics and functional traits in thermophilic digesters

A self-stabilizing microbial community lays the foundation of the efficient biochemical reactions of the anaerobic digestion (AD) process. Despite extensive profiling of microbial community dynamics under varying operating parameters, the effects of food waste (FW) to feeding sewage sludge (FSS) ratios on the microbial assembly, functional traits, and syntrophic interspecies interactions in thermophilic microbial consortia remain poorly understood. Here, we investigated the long-term impacts of the FW: FSS ratio on the thermophilic AD microbiome using genome-centric metagenomics. Both the short reads (SRs) assembly, and the iterative hybrid assembly (IHA) of SRs and nanopore long reads (LRs) were used to reconstruct metagenome-assembled genomes (MAGs) and four microbial clusters were identified, demonstrating different microbial dynamics patterns in response to varying FW:FSS ratios. Cluster C1-C3 were comprised of full functional members with genetic potentials in fulfilling empirical AD biochemical reactions, wherein, syntrophic decarboxylating acetogens could interact with methanogens, and some microbes could be energized by the electron bifurcation mechanism to drive thermodynamics unfavorable reactions. We found the co-existence of both acetogenic and hydrogenotrophic methanogens in the AD microbiome, and they altered their trophic groups to scavenge the methanogenic substrates in ensuring the methane generation in digesters with different FW:FSS ratios. Another interesting observation was that two phylogenetically close Thermotogota species showed a possible strong competition on carbon source inferred by the nearly complete genetic overlap of their relevant pathways.

Co-Combustion Characteristics And Ash Melting Behavior Of Sludge/High-Alkali Coal Blends

ABSTRACT Liquid slagging is an important solution for the problem of high-alkali coal slagging. The blending of low-melting-point fuel for combustion can effectively reduce the ash melting point of mixed fuel, improving the efficiency of liquid slagging. In this study, highly active sludge is mixed with Zhundong (ZD) coal. Then, co-combustion characteristics and ash melting behavior are studied by combining thermogravimetric analysis, thermodynamic analysis, ash melting analysis and ash composition analysis. The following results are observed. Ignition temperature is significantly reduced with an increase in sludge blending ratio, and combustion performance deteriorates rapidly when sludge proportion exceeds 20 wt.%. The burn out temperature initially decreases and then increases, reaching its minimum value when the sludge blending ratio is 10 wt.%. The blending of sludge causes the apparent activation of the sample to decrease, enhancing the combustion activity of the mixed fuel. The mixed fuel has lower ash melting point. A eutectic system with low melting point is produced due to the reaction of a large amount of sludge Fe2O3 with SiO2 in coal. The ash melting point is only 1080°C when 10 wt.% sludge is mixed. On the basis of the two considerations for improving combustion performance and reducing the melting point of ash, the recommended optimal blending ratio of sludge is 10 wt.%.

Submicron particle formation from co-firing of coal and municipal sewage sludge

With the increasing production of municipal sewage sludge (MSS) in China every year, the co-firing of MSS and pulverized coal is getting more and more widely applied in large coal-fired power plants. The co-firing of MSS and pulverized coal will produce a large amount of particulate matter (PM) emissions, especially submicron particles. In this paper, the formation characteristics of submicron particles in the co-firing process of coal and MSS were studied in a drop tube furnace. The influence of the furnace temperature and the addition ratio of sludge on the particle size distribution and element composition of submicron particles in MSS, pulverized coal combustion and co-firing was mainly studied. The experimental results show that the furnace temperature has an influence on the formation of PM0.4. For sludge combustion, increasing the furnace temperature will promote the formation of PM0.4. The main reason is that increasing the furnace temperature promotes the gasification of Si, S, Fe, and P to form the precursor of PM0.4 or PM0.4. At same furnace temperature, the volume concentration and mass concentration of PM0.4 produced from pulverized coal combustion are less than that of sludge. Different from sludge combustion, co-firing of pulverized coal and sludge has a synergistic effect on eliminating PM0.4 formation. Increasing the addition ratio of sludge can decrease the volume concentration and mass concentration of PM0.4. This is because that aluminosilicates formed during co-firing promotes the scavenge Si, Ca, Fe, thereby reducing the precursors of PM0.4 and the mass yield of PM0.4. Increasing the furnace temperature in co-firing can inhibit the formation of PM0.4. When the furnace temperature is between 1100 °C and 1300 °C, increasing the furnace temperature will reduce the Fe content and increase the content of Si, Ca, Na, K, and P in PM0.4. However, the reduction of Fe and the increase of Si, Ca, Na, K, and P in PM0.4 offset each other, resulting in an insensitive relationship between the mass yield of PM0.4 and the furnace temperature.

Biochemical assays of potential methane to test biogas production from dark fermentation of sewage sludge and agricultural residues

This study aims to study the methane generation potential (BMP tests) of different samples from the dark acid fermentation of sewage sludge:wine vinasse, and sewage sludge:wine vinasse:poultry manure. Specifically, mixtures of sewage sludge (S) and wine vinasse (V) were used in a 50:50 ratio and mixtures of sewage sludge and wine vinasse with 10 g/L of poultry manure (PM) (50:50 + 10 g/L) (S:V + PM). The goal was to determine the effect of the high ammonia concentrations in poultry manure when was used as co-substrate in the anaerobic methanogenic degradation of sewage sludge and vinasse. Results obtained show that the addition of 10 g/L of poultry manure to the SV mixture improves the production of methane generation, reaching values of 166 mL of accumulated methane. The SVPM mixture shows the highest purification percentages, with 63.90% TCOD removal, 79.51% SCOD removal and a yield of 52.05 mLCH 4 /gSV added . The SVPM test showed a higher concentration of microorganisms during the BMP test, although the population of microorganisms for the SV test was doubled and presented greater activity with values of 2.27 versus 1.73E-11 LCH 4 /Cells. • Bio-Methane Potential with the dark acid fermentation from a Bio-Hydrogen potential. • Bio-methane potential with sewage sludge, wine vinasse and poultry manure. • Anaerobic codigestion of sewage sludge, wine vinasse and poultry manure. • Poultry manure improves methane production and yield. • Anaerobic tridigestion presents better results than anaerobic bidigestion.

Preparation of municipal solid waste incineration fly ash-based ceramsite and its mechanisms of heavy metal immobilization

With an increase in municipal solid waste incineration (MSWI) fly ash and its dangerous characteristics, the manner of its disposal has caused widespread concerns. In this study, ceramsite was prepared by using MSWI fly ash, civil sludge, and contaminated soil as the main raw materials; then, a certain proportion of clay was added as an additive. The optimum MSWI fly ash content and sintering conditions were investigated, and the immobilization mechanisms of heavy metals were explored. Based on the obtained results, the optimum preparation conditions were a preheating temperature of 400 °C, a preheating time of 10 min, a sintering temperature of 1150 °C, and a sintering time of 20 min. Moreover, the optimal raw material ratio of MSWI fly ash, civil sludge, contaminated soil, and flint clay was 30%:40%:15%:15%. Under these optimum preparation conditions, the obtained ceramsite showed the following excellent performance parameters: a 1-h water absorption of 0.97%, bulk density of 998.7 kg/m3, and cylindrical compressive strength of 37.84 MPa. Furthermore, the leaching of heavy metals was far less than the standard GB5085.3-2007. The immobilization of heavy metals in the ceramsite was mainly caused by the glass phase encapsulation and the formation of new crystal phase with the heavy metals. In addition, the generation of aluminosilicates played a positive role in the immobilization of heavy metals. Thus, the reuse of MSWI fly ash by preparing fly ash-based ceramsite is one of the effective methods for reducing solid wastes.

Mechanical Characteristics and Micro-Mechanism of Modified Dredged Sludge Based on Calcium-Containing Solid Waste Used as Landfill Cover Materials

In order to prepare a new type of landfill covering material for closure, we used industrial calcium-containing waste (construction rubbish, slag, desulfurized gypsum and fly ash) to modify the dredged urban sludge. Shrink, unconfined compression, shear and infiltration tests were performed to obtain the volume shrinkage, compressive strength, shear strength and permeability coefficient of the modified sludge, as well as the permeability coefficient under the action of wet and dry cycles. Comprehensive characterization of the modified sludge using X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy detection methods, resulted in the hydration products, molecular groups and microstructure characteristics of the modified sludge and revealed the modification mechanism of calcium-containing waste to sludge. After natural curing for 28 d, the volume shrinkage rate of the modified sludge sample was 2.6~8.3%, the unconfined compressive strength was 7.9~14.5 MPa, the cohesion force c was 179~329 kPa, and the internal friction angle φ was 42.59~53.60°. After six wet and dry cycles, there were no cracks in the modified sludge; the permeability coefficient of the modified sludge reached stability at 0.84–11.1 × 10−7 cm/s; and the permeability coefficient of MS7 sample was less than 1 × 10−7 cm/s, which met the engineering anti-seepage requirements of the landfill closure cover. The industrial calcium-containing waste by alkali formed C–S–H and C–A–S–H gelled geopolymer, which filled the gaps between soil particles to form a strong soil cement skeleton. Therefore, the mix ratio of sludge:construction waste:slag:fly ash:desulfurized gypsum was 50:22:15:8:5. Calcium-containing solid waste modified sludge can be used as a cover material for landfill closure.

Migration Behaviors of As, Se and Pb in Ultra-Low-Emission Coal-Fired Units and Effect of Co-Firing Sewage Sludge in CFB Boilers

The migration behaviors of As, Se and Pb in ultra-low-emission coal-fired units were investigated and the effect of co-firing of sewage sludge and coal was explored in circulating fluidized-bed (CFB) boiler units. Samples of feed fuel including coal and sewage sludge, fly ash, bottom slag and desulfurization slurry were collected from five CFB units with a capacity between 150 MW and 350 MW and two pulverized coal boiler (PC) units with a capacity of 350 MW and 600 MW. The majority of As, Se and Pb in coal is released during coal combustion and enriched in fly ash. As, Se and Pb in fly ash and bottom slag are associated with inorganic matter, of which As, Se and Pb associated with silicates and aluminosilicates account for more than 60%. In the wet flue gas desulfurization (WFGD) unit, more than half of the As, Se and Pb migrates to the solid fraction and the concentrations of As, Se and Pb in fine solid particles are much higher than those in coarse solid particles and the liquid fraction. The proportions of exchangeable As, Se and Pb or associated with organic matter in gypsum are higher than those of fly ash and bottom slag. According to the two studied CFB units with blending ratios of sewage sludge below 10%, co-firing with sewage sludge has little effect on the migration and transformation characteristics of As, Se and Pb. Under a long-term acidic leaching environment, Pb in combustion by-products is in the range of low risk, while As and Se are in the range of medium risk.

Optimization mixing ratio of the brewery waste water sludge and coal as energy source for cement industry and fuel ash effect on the raw material composition

Brewery waste water produces sludge with high organic content, which required proper treatment before disposal. The sludge is disposed to landfill creating contamination to the ground water and surface water due to high organic content. Also, it increases the salinity of crops and the environment. Since it has potential for energy production, it can be used in the country's coal-dependent cement industry due to its energy content. The objective of this study was to characterize brewery wastewater sludge and coal, to determine the optimum mix ratio and to see the effect of mixture fuel ash content on raw mix design. Characterization of coal using American Standard Testing Material 2009 and sludge using the World Health Organization method was done and also calorific value with different mixing ratio of coal and sludge determined by a bomb calorimeter in order to find the optimum mix. By using proportionating calculation, determining the effect of mixture fuel ash on the clinker and proportion of raw materials used is done. Brewery wastewater sludge has high moisture content and volatile matter compared to coal. Also, its ash content is higher than coal's. The caloric value of brewery wastewater sludge will not allow for using it without mixing. It is found that 70% coal and 30% sludge is the optimum mix ratio. Its high amount of SiO2 (45%), Al2O3 (14%), and Fe2O3 (11%) makes it possible to substitute some portion of clay and sand stone while our lime feed increases as a result. Since mixture fuel ash content is similar with cement raw materials, brewery wastewater sludge is a good alternative for the cement industry.

Response surface methodology to optimize ultrasonic-assisted extraction of crude oil from oily sludge

This study is the first to use a response surface method to optimize the main parameters of ultrasonic-assisted recovery of oil from oily sludge. The solvent with the highest oil recovery (xylene) and most suitable process (Ultrasonic Assisted Extraction) were first selected based on the highest oil recovery rate. Then, single-factor experiments were performed to determine the best parameter range of solvent sludge ratio, frequency, duration, and temperature. Box-Behnken response surface methodology was used to study the influence of each variable on oil recovery. Solvent sludge ratio, frequency, and duration were found to have significant effects. The model optimization results show that the best conditions for Ultrasonic Assisted Extraction are as follows: a solvent to sludge ratio of 7.56:1, frequency of 31.48 kHz, duration of 23.67 min, and temperature of 45.87 °C. Under optimum conditions, the oil recovery predicted by the model and the actual oil recovery were 87.21 and 83.77%, respectively. The relative error between the predicted and actual values was 3.44%. These results indicate that the model results are reliable. Finally, the characteristics of the recovered oil and residue were analyzed. This research provides the possibility to utilize difficult-to-handle crude oil tank bottom sludge.

Reaction Characteristics of Hydrogen-Rich Syngas Production by Sludge/Coal Cogasification Based on the Iron-Based Oxygen Carriers

With the acceleration of industrialization and urbanization in China, wastewater treatment is increasing yearly. As a by-product of wastewater treatment, the gasification of sludge with coal in chemical looping process is a clean and efficient conversion technology. To explore the reaction behavior of cogasification of sludge and coal with iron-based oxygen carriers (OCs) for producing hydrogen-rich syngas, the experiment of cogasification using Fe2O3/Al2O3 as OC in a fluidized bed reactor was conducted. The result showed that the volume percentage of hydrogen (H2) and syngas yield is proportional to the amount of sludge added. The optimal operation conditions were: temperature at 900 °C, the mass ratio of OC to coal at 5.80 and mass ratio of sludge to coal at 0.2. Under this operating condition, the volume percentage of H2 and syngas yield in the flue gas was 75.6 vol% and 97.5 L·min-1·kg-1, respectively. Besides, the OC showed a stable reactivity in the sixth redox cycle with added sludge. However, the reactivity of OC significantly declined in the seventh and eighth redox cycles. It was recovered when the ash was separated. The decrease in the specific surface area of the OC caused by ash deposition is the main reason for the decline in its reactivity. The kinetic analysis showed that the random pore model describes the reaction mechanism of sludge/coal chemical looping gasification (CLG). The addition of sludge can reduce the activation energy of coal CLG reaction, accelerate the gasification reaction rate and increase the carbon conversion.

Experience of using sewage sludge in soil for green building

Wastewater sludge from municipal wastewater treatment plants in Nizhny Novgorod and soils based on them, prepared with different ratios of sludge, sawdust and peat, have been investigated. Sewage sludge-based soils contain plant nutrients and are suitable for use as fertilizing materials in green building. Under the conditions of a three-year lysimetric experiment on cereal lawn grasses, a significant efficiency of organic soils was noted in comparison with traditional soils. The lawn maintenance regime revealed differences in the mixtures of fertilizing materials in terms of the effect on the productivity of the phytocenosis. Use of sewage sludge containing large amounts of heavy metals as one of the soil components undoubtedly leads to increase in the amount of these toxic elements in the soil as a whole.

Simulation and Optimization of Anaerobic Co-Digestion of Food Waste with Palm Oil Mill Effluent for Biogas Production

Food waste (FW) utilized as substrate for anaerobic digestion (AD) to produce biogas is promising. Simultaneously, waste is handled and value-added products such as biogas and fertilizer are produced. Palm oil mill effluent (POME) is used as the co-substrate. This study aims to simulate the complete process flow of anaerobic co-digestion (AcoD), consisting of pre-treatment of feedstock, biogas upgrading, wastewater treatment and sludge dying using SuperPro Designer. Parameters, namely hydraulic retention time (HRT), recycle ratio of sludge, water to FW ratio (kg/kg) and co-substrate to FW ratio (kg/kg), would affect the performance of digester. The optimization of these parameters is performed using Design-Expert software, involving response surface methodology (RSM). The effects on responses such as methane flow, chemical oxygen demand (COD) and volatile solid (VS) removal efficiencies are analyzed. In treating 25,000 kg/h of feed, the optimized values for HRT, recycle ratio, water to feedstock ratio, POME to FW ratio are 37.2 days, 0.381, 0.027 and 0.004, respectively. The methane yield is 0.30 L CH4/g of COD removed, with COD and VS removal efficiencies of 81.5% and 68.9%, respectively. The project is profitable, with a payback period of 6.14 years and net present value (NPV) of $5,680,000. A comprehensive understanding of AD matures it for commercialization purposes.

Enhanced removal of ibuprofen by heterogeneous photo-Fenton-like process over sludge-based Fe3O4-MnO2 catalysts

Abstract Heterogeneous photo-Fenton-like catalysts with low cost, little hazard, high effectiveness and facile separation from aqueous solution were highly desirable. In this study, sludge-based catalysts combining nano Fe3O4-MnO2 and sludge activated carbon were successfully synthesized by high-temperature calcination method and then characterized. These synthetic materials were applied to remove ibuprofen in the heterogeneous photo-Fenton process. The preparation conditions of sludge-based catalysts optimized by orthogonal experiments were 2.0 M of ZnCl2, a temperature of 500 °C, a pyrolysis time of 60 min, and a sludge ratio: Fe3O4-MnO2 of 25:2. In batch experiments, the optimal experimental conditions were determined as catalyst dosage of 0.4 g·L−1, hydrogen peroxide concentration of 3.0 mL·L−1, pH value of 3.3, and contact time of 2.5 h. The degradation rate sludge/Fe3O4-MnO2 catalyst to ibuprofen is up to 95%. The removal process of ibuprofen fitted the pseudo-second-order kinetic model, and the photocatalytic degradation process was the main factor controlling the reaction rate. The catalytic mechanism was proposed according to the Fourier transform infrared analysis and mass spectrometry product analysis; it was mainly attributed to the interaction between hydroxyl groups and benzene rings.