Volatile Solids Reduction Research Articles

Effect of Effluent Recirculation on Biogas Production Using Two-stage Anaerobic Digestion of Citrus Waste.

Citrus waste is a promising potential feedstock for anaerobic digestion, yet the presence of inhibitors such as d-limonene is known to limit the process. Effluent recirculation has been proven to increase methane yield in a semi-continuous process for recalcitrant material, but it has never been applied to toxic materials. This study was aimed to investigate the effect of recirculation on biogas production from citrus waste as toxic feedstock in two-stage anaerobic digestion. The first digestion was carried out in a stirred tank reactor (STR). The effluent from the first-stage was filtered using a rotary drum filter to separate the solid and the liquid phase. The solid phase, rich in hydrophobic D-limonene, was discarded, and the liquid phase containing less D-limonene was fed into the second digester in an up-flow anaerobic sludge bed (UASB) reactor. A high organic loading rate (OLR 5 g VS/(L·day)) of citrus waste was fed into the first-stage reactor every day. The effluent of the first-stage was then fed into the second-stage reactor. This experiment was run for 120 days. A reactor configuration without recirculation was used as control. The result shows that the reactor with effluent recirculation produced a higher methane yield (160–203 NmL/g·VS) compared to that without recirculation (66–113 NmL/g·VS). More stable performance was also observed in the reactor with recirculation as shown by the pH of 5–6, while without recirculation the pH dropped to the range of 3.7–4.7. The VS reduction for the reactor with recirculation was 33–35% higher than that of the control without recirculation. Recirculation might affect the hydrolysis-acidogenesis process by regulating pH in the first-stage and removing most of the D-limonene content from the substrate through filtration.

Temperature-Phased Biological Hydrolysis and Thermal Hydrolysis Pretreatment for Anaerobic Digestion Performance Enhancement

Thermal hydrolysis (TH) and biological hydrolysis (BH) are two main and growing anaerobic digestion pretreatment technologies. In this study, municipal wastewater sludge samples were collected from the Guelph Wastewater Treatment Plant (WWTP) in Ontario, Canada. The effects of temperature on BH treatment, including BH at 42 °C (BH42), 42 °C followed by 55 °C (BH42+55), 55 °C followed by 42 °C (BH55+42), and 55 °C (BH55) were evaluated for anaerobic digestion performance enhancement and compared with TH treatment at 165 °C. The TH, BH42, BH42+55, BH55+42, and BH55 treatments caused the reduction of volatile suspended solids (VSS) by 22.6%, 17.5%, 24.6%, 23.1%, and 25.9%, respectively. The soluble chemical oxygen demand (sCOD) content of the sludge increased by 377.5%, 323.8%, 301.3%, 286.9%, and 221.7% by the TH, BH55, BH42+55, BH55+42, and BH42 treatments, respectively. Volatile fatty acids (VFA) constituted around 40% of the sCOD in the BH-treated sludge and 6% in the TH-treated sludge. The cumulative methane yields (NmLCH4/g COD fed) of sludge treated by BH55+42 and TH were respectively 23% and 20% higher than that of the untreated sludge. For BH pretreatment, sludge treated by BH55+42 produced more methane than those treated by BH42+55, BH55, and BH42. The methane yields of the combined sludge treated by the TH and BH55+42 treatments were in the ranges of 248.9 NmLCH4/g COD to 266.1 NmLCH4/g COD fed, and 255.3 NmLCH4/g COD to 282.2 NmLCH4/g COD fed, respectively.

Effect of pre-treatments on biological methane potential of dewatered sewage sludge under dry anaerobic digestion

The aim of the study is to enhance hydrolysis of dewatered sewage sludge to tackle the problem of low biological methane potential (BMP) and low efficiency of dry anaerobic digestion. Different pre-treatment i.e. physical (ultrasonication), chemical (acid, ozone) and combined (ultrasonication-ozone) methods were investigated and evaluated in terms of BMP and biodegradation. Ultrasonic pre-treatment had the best result among the single technologies, the BMP increased by 104.7%, while total solid (TS), volatile solid (VS) and chemical oxygen demand (COD) reduction were improved by 30.1%, 36.9% and 33.9%, respectively, over control. Combined pre-treatment (ultrasonication-ozone) showed more significant enhancement than single methods as evidenced by 138.2% higher BMP and 53.7%, 63.7% and 57.3% more reduction in TS, VS, COD, respectively, over control. The BMP increment positively correlated either with energy input, concentration or dose of pre-treatment applied. Among the tested methods, the physical pre-treatments out-compete chemical ones. Ultrasonic combined with ozone pre-treatment technology has good energy and economic feasibility.

Enhancement of dewaterability and heavy metals solubilization of waste activated sludge conditioned by natural vanadium-titanium magnetite-activated peroxymonosulfate oxidation with rice husk

In this work, natural vanadium-titanium magnetite-activated peroxymonosulfate (VTM-PMS) oxidation coupled with rice husk (RH) as skeleton builder (VTM-PMS-RH) was employed to enhance sludge dewaterability for the first time. The optimal dosages of PMS, VTM, and RH were 200 mg/g total suspended solids (TSS), 1 g/g TSS, and 200 mg/g TSS, respectively. Under optimal conditions, capillary suction time (CST) reduction and water content of sludge cake (WC) were 82.1% and 72.9% after VTM-PMS conditioning, respectively, which further reached the values of 94.8% and 63.4% when coupled with RH treatment. Cycle experiments demonstrated that VTM reusability in VTM-PMS system for dewatering sludge was desirable. Based on sludge physicochemical properties after conditioning (i.e., extracellular polymeric substances (EPS), zeta potential, dissolved organic carbon (DOC), total nitrogen (TN), and volatile suspended solids (VSS) reduction), VTM-PMS oxidation shows the merits of EPS degradation, sludge disintegration, and charge neutralization. In addition, the transformation behaviors of heavy metals (HMs) in sludge after conditioning were investigated according to total HMs contents, speciation distribution, and leaching tests. Through conditioning, total HMs contents (Cu, Zn, Cr, and Pb) in liquid phase increased while were adverse in solid phase. The leaching toxicity reductions were 78%, 83%, 60%, and 100% for Cu, Zn, Cr, and Pb, respectively, obtained by VTM-PMS-RH conditioning. Meanwhile, the chemical speciation distribution of HMs in sludge was changed and transformed into more stable forms, as well as the environmental risk of HMs decreased. These results suggest that VTM-PMS-RH process has a synergistic contribution to the environmental risk reduction of HMs and their immobilization enhancement. Therefore, VTM-PMS-RH process is a promising alternative for sludge conditioning in terms of the enhancement of dewaterability and HMs solubilization.

Production of lipid-containing algal-bacterial polyculture in wastewater and biomethanation of lipid extracted residues: Enhancing methane yield through hydrothermal pretreatment and relieving solvent toxicity through co-digestion

The feasibility of generating a lipid-containing algal-bacterial polyculture biomass in municipal primary wastewater and enhancing biomethanation of lipid-extracted algal residues (LEA) through hydrothermal pretreatment and co-digestion with sewage sludge (SS) was investigated. In high-rate algal ponds, the polyculture of native algal and bacteria species demonstrated a monthly average net and gross biomass productivity of 30 ± 3 and 36 ± 3 gAFDW m−2 day−1 (summer season). The algal community was dominated by Micractinium sp. followed by Scenedesmus sp., Chlorella sp., pennate diatoms and Chlamydomonas sp. The polyculture metabolic activities resulted in average reductions of wastewater volatile suspended solids (VSS), carbonaceous soluble biochemical oxygen demand (csBOD5) and total nitrogen (Ntotal) of 63 ± 18%, 98 ± 1% and 76 ± 21%, respectively. Harvested biomass contained nearly 23% lipid content and an extracted blend of fatty acid methyl esters satisfied the ASTM D6751 standard for biodiesel. Anaerobic digestion of lipid extracted algal residues (LEA) demonstrated long lag-phase in methane production of 17 days and ultimate methane yield of 296 ± 2 mL/gVS (or ~50% of theoretical), likely because to its limited biodegradability and toxicity due to presence of the residual solvent (hexane). Hydrothermal pretreatment increased the ultimate methane yield and production rate by 15–30% but did not mitigate solvent toxicity effects completely leading to less substantial improvement in energy output of 5–20% and diminished Net Energy Ratio (NER < 1). In contrast, co-digestion of LEA with sewage sludge (10% to 90% ratio) was found to minimize solvent toxicity and improve methane yield enhancing the energy output ~4-fold, compared to using LEA as a single substrate, and advancing NER to 4.2.

Increase of the oxygen vacancy component in bridgmanite with temperature

The oxygen vacancy (OV, MgAlO2.5) contents in bridgmanite with periclase and/or a calcium ferrite-type MgAl2O4–Mg2SiO4 phase (CF-phase) were investigated at temperatures of 1700, 2000, and 2400 K and a pressure of 27 GPa using an ultrahigh-pressure multi-anvil press. The OV content increases significantly with increasing temperature by consuming coexisting periclase and the charge-coupled (CC, AlAlO3) component in bridgmanite. The increase in OV component at high temperature is promoted by its high entropy. The CC components increase largely with temperature compared with the OV content in bridgmanite coexisting with CF-phase and periclase because the partition coefficient of Mg and Al between bridgmanite and CF-phase approaches unity because of the mixing entropy. The partial molar volumes of OV and CC bridgmanite endmembers at ambient conditions were constrained to be 26.64 and 25.79 cm3/mol, respectively, with densities of 3.428 and 3.955 g/cm3. By assuming linear relationships between wave velocities and density, the OV component may therefore cause a velocity reduction by one order of magnitude larger than the CC component at constant Al content in bridgmanite. The concomitant increase and decrease in OV and CC contents with temperature enhance VP and VS reductions by 0.7% and 2.5% in addition to anharmonic effects. The OV component in bridgmanite in subducted slabs is zero because of low temperature, and the transport of water and argon trapped by the OV component into the lower mantle by bridgmanite is therefore not expected. The storage capacity of these volatiles in subducted slabs will thus be significantly lower than the warm ambient mantle. Since the OV component is expected to enhance diffusion creep, the present results may explain slab stagnation in the mid-mantle due to low OV contents at low temperature, and vertically straight plumes in the lower mantle due to high OV contents at high temperature.

Microbial acclimatization to lipidic-waste facilitates the efficacy of acidogenic fermentation

Lipidic-waste such as fat, oil, and grease (FOG) are promising substrates for achieving higher bioenergy yields. An inadequate presence of an effective microbiome in the anaerobic digesters is the bottleneck for the proper utilization of FOG. Gradual introduction of FOG (0.2%, 1.2%, and 2.4% as volatile solids) in acidogenic fermentation showed a significant improvement in hydrogen yield (72%), compared to the control, after 2.4% FOG loading. Volatile solid (VS) reduction reached up to 65% in high FOG reactors with complete removal of major unsaturated fatty acids. Removal of saturated fatty acids increased to 90%. Improvement in hydrogen productivity (46 mL d−1) occurred during step-wise loading of 2.4% FOG to the acclimatized microbiome. The metabolic shift toward carboxylic chain elongation produced C4 and C6 fatty acids at concentrations of 1.61 mM and 0.90 mM, respectively in the acidogenic reactors. High-throughput sequencing of 16S rRNA amplicons revealed that the acclimatization process enriched the phylum Firmicutes (90%), followed by Bacteroidetes (12%) and Cloacimonetes (11%). The abundance of these phyla and their respective genera confirmed their preeminent role in hydrolysis, hydrogenogenic acidogenesis, and carboxylic chain elongation to produce hydrogen and C4–C7 fatty acids. Thus, we suggest that the improvement of hydrogen production using a microbiome acclimatized to FOG, and simultaneous production of high value organics (C4–C7 fatty acids), could facilitate the greater efficacy of the acidogenic fermentation.

An Insight into the Anaerobic Co-digestion of Municipal Solid Waste and Food Waste: Influence of Co-substrate Mixture Ratio and Substrate to Inoculum Ratio on Biogas Production.

The unbalanced nutrients of municipal solid waste (MSW), particularly high carbon contents, were regarded as a major limiting factor to anaerobic digestion process. In this study, the addition of MSW in food waste (FW) feedstock to have a balanced C/N ratio was studied. Different co-substrate mixtures with C/N ratio of 20 to 40 were subjected to anaerobic batch experiment at lab scale, under mesophilic conditions. The biogas production decreased with the increase in C/N ratio due to insufficient availability of organic nitrogen for anaerobic microbial growth. Specific biogas and methane yields were observed to be 827 and 474.44mLg-1VS, respectively, with volatile solids (VS) reduction rate of 88%, at C/N ratio of 20. Furthermore, the effect of the substrate to inoculum (S/I) ratio on digester performance was also studied. The biogas production decreased with the increase in S/I ratio due to the formation of more volatile fatty acids (VFAs) which led to decrease in pH and accumulated unionized ammonia-N. Specific biogas and methane yields were recorded to be 655 and 410.20mLg-1VS, with 64% rate of biodegradability at S/I ratio of 0.5. Kinetics and statistics study showed that the higher S/I ratio could lead to VFA accumulation and result in low methane yield.

Crude glycerin in co-composting with laying hen manure reduces N losses

ABSTRACT: The composting of laying hen manure is an efficient way of treating waste and producing an organic fertilizer with excellent characteristics; however, the high N losses reduce its concentration in the resulting fertilizer. Associating this residue with crude glycerin (CG) promotes a better C:N ratio and contributes to higher N retention during composting, with improvements in solids reduction and production of organic fertilizer with higher concentration of this nutrient. We carried out this research considering the hypothesis that adding CG – a byproduct of biodiesel production – to laying hen waste composting provides better N retention in the fertilizer generated. Increasing CG doses (0, 3, 6, 9, and 12 % in relation to the fresh mass in the windrows) were added to the laying hen manure with windrows composted for 70 days. A reduction by 100 % in total and thermotolerant coliforms occurred at all levels of CG addition. The maximum reductions in total (TS) and volatile (VS) solids were 64 and 76 %, respectively, and occurred with the addition of 6 % CG. The windrows that did not receive CG had higher N losses during the process (32 %) while the highest N concentration in the compost was 5 % at 6 % CG. We identified that adding 6 % CG to the laying hen manure in co-composting increases the reductions in TS and VS and provides higher N retention, which improves the quality of the organic fertilizer.

Phagotrophic microalgae production from waste activated sludge under non-sterile conditions

In this study waste activated sludge (WAS) was sonicated to release bacteria-sized volatile solids (VS) from flocs, after initial pH adjustment to 10 for higher energy efficiency. The released VS supported growth of phagotrophic alga Ochromonas danica. Initial-rate growth experiments confirmed the Monod-type kinetics but the specific cell growth rate, μ, correlated with the prey-to-predator ratio, i.e., the ratio of (fed VS concentration)-to-(initial O. danica concentration), significantly better than with the VS alone, as the typical Monod dependency on soluble substrates. The best-fit kinetics had the following parameters: μmax = 0.198 h−1 and KM = 1.056 (g-VS/g-algae). Post-sonication reflocculation could render particles too large to ingest by O. danica; therefore, pH and VS effects on reflocculation were investigated. Batch cultivations were then conducted in fermentors at pH 5, under nonsterile conditions. Algae number reached 8.86 × 1010 L−1 after 20 h, corresponding to ∼2.3 g/L dry-weight and volumetric algae productivity of 2.8 g/L-day. VS reduction was 38%, giving an O. danica VS yield of 44.5%. The ultrasonication-algae process can be used to produce algae while achieving at least partial WAS treatment.

Thermophilic Anaerobic Digestion: Enhanced and Sustainable Methane Production from Co-Digestion of Food and Lignocellulosic Wastes

This article aims to study the codigestion of food waste (FW) and three different lignocellulosic wastes (LW) (Corn stover (CS), Prairie cordgrass (PCG), and Unbleached paper (UBP)) for thermophilic anaerobic digestion to overcome the limitations of digesting food waste alone (volatile fatty acids accumulation and low C:N ratio). Using an enriched thermophilic methanogenic consortium, all the food and lignocellulosic waste mixtures showed positive synergistic effects of codigestion. After 30 days of incubation at 60 °C (100 rpm), the highest methane yield of 305.45 L·kg−1 volatile solids (VS) was achieved with a combination of FW-PCG-CS followed by 279.31 L·kg−1 VS with a mixture of FW-PCG. The corresponding volatile solids reduction for these two co-digestion mixtures was 68% and 58%, respectively. This study demonstrated a reduced hydraulic retention time for methane production using FW and LW.

Feasibility Study of Chromium Removal from Paint Sludge with Biological Sludge, Using Vermicompost by Eisenia fetida (Case Study: Saipa Automotive Industry)

Background: During the paint spraying process in the automotive industry, a variety of wastes, including a large amount of paint sludge is produced, which contains a variety of hazardous substances, such as BTEX and heavy metals. The aim of the present study was vermicomposting of paint sludge with sewage sludge and Eisenia fetida as earthworm spices for reduction of heavy metals. Objectives: Vermicomposting process employing earthworms is increasingly being used for conversion of both sewage and some industrial wastes to reduced heavy metals and volatile solid content in bulk of solid wastes. Therefore, in this study, feasibility of chromium removal from paint sludge by using Eisenia fetida worms was investigated. Methods: In this study, the quantitative and qualitative characteristics of paint and biological sewage sludge waste were determined in terms of Cr+6, moisture content, nitrogen and carbon, C/N ratio, pH and temperature. Then the paint sludge was mixed in various proportions with the thickening biological sewage sludge of Saipa’s sewage treatment plant. The decomposition time for the vermicompost samples for each run was 90 days. In order to analyze various parameters, including Cr+6 and volatile solids reduction, sampling from each pilot was performed on 1, 15, 30, 50, 70 and 90 days. The Cr+6 measurements were performed using the AASM method. The paint sludge and sewage sludge were mixed in different ratios. After the mixing, 500 adult Eisenia fetida earthworms were introduced to each box. Results: The results showed that the optimum removal rate for Cr+6 was found in the mixing ratio of 6 kg of biological sludge with 600 g of paint sludge and in this ratio, the amount of Cr+6 concentration fell from 6 mg/kg to less than 0.2 mg/kg in 90 days. In addition, in the same ratio of sludge mixing, the C/N ratio ranged from about 27 on the first day to 14.3 on day 90 and the pH decreased from 7.8 on the first day to 7.3 on the 90th day. Volatile solids decreased from 80.4% on the first day to 37% on the 90th day. Conclusions: Vermicomposting is a good alternative for treating paint sludge with biological sludge, and is advantageous for reduction of pollutants purposes. Research was carried out on bioavailability of heavy metals such as Cr+6 during vermicomposting for 90 days using Eisenia fetida earthworms. Finally, the results showed that, Eisenia fetida could eliminate Cr+6 in low levels.

Ampelodesmos mauritanicus pyrolysis biochar in anaerobic digestion process: Evaluation of the biogas yield

The integration of different conversion technologies can strongly contribute to the biomass potential exploitation. To this aim, the use of intermediate pyrolysis biochar is analyzed in this paper as an alternative co-substrate in anaerobic digestion. The specie Ampelodesmos mauritanicus has been specifically chosen in this case for its capacity to tolerate, accumulate and, in some cases, degrade organic and inorganic pollutants. The biochar, produced under intermediate pyrolysis conditions at 450 °C, 500 °C and 550 °C, has been here considered for a biomethane potential assessment. The intermediate pyrolysis process improves the herbaceous bioavailability and promotes the microbial activity by reducing the digestion lag phase. Three reactors, namely B450, B500 and B550, have been considered in this study. Acclimatized cow manure from food wastes digestion has been used as inoculum with 5 g of biochar. The reactors have been continuously monitored for 15 days keeping the temperature fixed at 37 °C. Excluding the inoculum contribution, an accumulated methane production of 465–540.4 ml CH4/g-VS has been measured with an LHV evaluated in the range 25.8–26.9 MJ/kg. The modified Gompertz equation has been then used to describe the influence of biochar production temperature on methane conversion. A lag phase of 1.8, 2.2 and 3.8 days respectively for B450, B500 and B550, has been estimated showing an inverse proportionality to the biochar production temperature. The biomass to biogas energy conversion analysis reveals a reduction in the efficiency with the biochar production temperature increase. This fact is attributed to the steep reduction in volatile solids occurring by increasing the pyrolysis process severity. As a whole, the paper present a novel approach to possibly combine phytoremediation and production of renewable energy by using Ampelodesmos mauritanicus.

Biochemical methane potential (BMP) test for Ageratum conyzoides to optimize ideal food to microorganism (F/M) ratio

Ageratum conyzoides is a rapidly colonizing invasive alien terrestrial weed that has become troublesome all over the world. This noxious weed shows adverse effects on the rice fields, which is a staple food crop in many countries, and it increases the productivity cast, hence this weed needs to be managed in a systematic way. This study was performed to identify the ideal food to microorganism (F/M) ratio for maximum methane production. BMP assay revealed that, F/M ratio 2 acquired maximum biogas production from the anaerobic digestion of A.conyzoides biomass with cow dung as the microorganism source. Highest methane production was achieved on 25th day around 205 ± 10 mL CH4/g VS (volatile solid) and cumulative biogas production reach up to (4994 ± 25 mL). 80% of the total biogas produced was achieved within the first 30 days. Highest Volatile solid reduction was observed in F/M ratio 2 (45.30%) as compared to other ratios. Volatile fatty acid (VFA) and Soluble chemical oxygen demand (sCOD) also found to be highest in F/M ratio 2. In kinetic study, M value was found to be 4.0000 L CH4 in ratio 2.

Anaerobic co-digestion of animal manure at different waste cooking oil concentrations

ABSTRACT: This study aimed to obtain the best dose of waste cooking oil inclusion for the co-digestion of substrates prepared with dairy cattle and swine manure in order to maximize solids reductions and biogas yield. Analyses of total solids (TS), volatile solids (VS), and neutral detergent fiber (NDF) were performed during the loading and unloading of digesters, while biogas yield was measured twice a week. The maximum reduction in VS (51.4%) was reached with the inclusion of up to 54.6g waste cooking oil.kg manure-1. Maximum NDF degradation occurred with inclusions of up to 69.4g waste cooking oil.kg manure-1. Inclusions of up to 64g of waste cooking oil.kg manure-1 provided specific biogas yield of 291.4 and 251.0L biogas.kg VS-1 added to substrates with swine and cattle manure, respectively. Adding oil at doses between 45.1 and 69.4g waste cooking oil kg manure-1 to substrates composed of cattle or swine manure maximizes reductions of solids and fibrous constituents and enhances specific biogas yield. Furthermore, swine manure supports higher doses of waste cooking oil.

Developing an anaerobic digester with external Zeolite filled column for enhancing methane production from swine manure – A feasibility study

ABSTRACTDevelopment of digesters with an external zeolite column facilitates the convenient removal of the zeolite with TAN, without disturbing the continuous anaerobic digestion process. A digester with an inside zeolite bed (In-Zeo) and digester without adding zeolite (No-Zeo) were employed to compare the process performance with digester with external zeolite column (EX-Zeo). The cumulative, CH4 yields were 5% and 15% greater in the EX-Zeo, and the In-Zeo digesters respectively compared to the No-Zeo digesters. Also, the % VS reduction was 49%, 55% and 41%, respectively in the Ex-Zeo, In-Zeo and No-Zeo digesters. The results indicated that treatment with 7% zeolite during anaerobic digestion has the potential to improve biodegradation of swine manure. The addition of zeolite appeared to reduce TAN from the digestate, thereby enhancing the CH4 yield. Zeolite could be used either internally or externally to enhance CH4 production through anaerobic digestion of swine manure.

Characterization of bacterial community structure during in-vessel composting of agricultural waste by 16S rRNA sequencing.

Bacterial diversity during in-vessel (rotary drum) composting of agricultural waste was characterized using NGS-based 16S rRNA sequencing for microbial identification. The activity of the bacteria was observed to vary with the composting materials and degradation pattern. Taxonomic hits distribution at domain level revealed that 89.5% sequences belonged to bacteria, 9% to eukaryota followed by 1.4% archaea during drum composting. The lowest common ancestor (LCA) classification plot showed the high abundance of the phylum proteobacteria followed by actinobacteria in compost sample. Taxonomic hit distribution at family level showed that compost sample was enriched with Thermomonosporaceae. Thermomonospora curvata is an aerobic, cellulolytic, thermophilic Gram-positive bacterium which produces a number of industrially important compounds, i.e., cellulase, alpha-amylase, and polygalacturonate lyase. Thermomonospora family of bacteria play a major role in organic matter degradation during composting. Hence, in the present study species such as Actinomadura vinacea, Thermomonospora curvata, Actinoallomurus spadix, Actinomadura rubrobrunea. T. curvata were identified from the compost mixture, which can utilize many organic compounds such as cellulose starch, xylose or pectin. The other biggest group in compost sample was Actinobacteria with Thermoleophilum album as the most abundant species followed by Collinsella aerofaciens. The compost was stabilized with higher volatile solids reduction, lower OUR (4.49mg/g VS/day) and CO2 (2.28mg/g VS/day) values at the end of 20days. The final compost was observed with 2.31% of TKN and 4.3% of phosphorus. Finally the results indicate that degradation of agricultural waste using drum composter was dominated by Bacilli, γ, β-proteobacteria, and actinobacteria.

Kinetic Modeling for Bioaugmented Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste by Using Fe3O4 Nanoparticles

Kinetic modeling helps in the process designing, reactor dimensioning, and up scaling of any system. A kinetic study of batch anaerobic digestion (AD) of food waste (FW), which is the organic fraction of municipal solid waste was conducted. Iron oxide (Fe3O4) nanoparticles (NPs) were added and their impact on methane generation and volatile solids (VS) removal was modeled through the existing kinetic models. AD of FW was carried out at a mesophilic temperature (37 ± 0.5 °C) for 60 days. Four different concentrations of Fe3O4 NPs, at 50, 75, 100, 125 mg L−1, were added, and the performance was evaluated by comparing it with the control (without NPs) and by kinetic modeling. The rate of reactions (k) was evaluated by using pseudo-first-order reaction kinetics by considering the initial and final data. The modified Gompertz model, Logistic, and Transference functions were fitted to the cumulative methane generation. The best fits of models were statistically determined by estimating the coefficient of correlation (R2), standard deviation residual (SDR) and least significant difference tools. The k values for all concentrations and the control were determined to be 6.1 × 10−3, 1.4 × 10−2, 1.8 × 10−2, 9.6 × 10−3, and 7.1 × 10−3 (day−1), respectively. The results of the study indicated that the modified Gompertz model produced a perfect fit with highiest R2 and the smallest value of SDR. Furthermore, more than 50% of VS reduction was achieved with the addition of 75 mg L−1 Fe3O4 NPs. The modified Gompertz model predicted the experimental results with a higher R2 and a lower SDR value at all concentrations of NPs.

Fuzzy multi-objective optimization case study based on an anaerobic co-digestion process of food waste leachate and piggery wastewater

This paper presents the development and evaluation of fuzzy multi-objective optimization for decision-making that includes the process optimization of anaerobic digestion (AD) process. The operating cost criteria which is a fundamental research gap in previous AD analysis was integrated for the case study in this research. In this study, the mixing ratio of food waste leachate (FWL) and piggery wastewater (PWW), calcium carbonate (CaCO3) and sodium chloride (NaCl) concentrations were optimized to enhance methane production while minimizing operating cost. The results indicated a maximum of 63.3% satisfaction for both methane production and operating cost under the following optimal conditions: mixing ratio (FWL: PWW) – 1.4, CaCO3 – 2970.5 mg/L and NaCl – 2.7 g/L. In multi-objective optimization, the specific methane yield (SMY) was 239.0 mL CH4/g VSadded, while 41.2% volatile solids reduction (VSR) was obtained at an operating cost of 56.9 US$/ton. In comparison with the previous optimization study that utilized the response surface methodology, the SMY, VSR and operating cost of the AD process were 310 mL/g, 54% and 83.2 US$/ton, respectively. The results from multi-objective fuzzy optimization proves to show the potential application of this technique for practical decision-making in the process optimization of AD process.

Start-up phase of a two-stage anaerobic co-digestion process: hydrogen and methane production from food waste and vinasse from ethanol industry

The start-up conditions of mesophilic anaerobic co-digestion of restaurant food waste and vinasse, a waste from sugarcane industry, was investigated for efficient biogas production. A pilot plant, containing two reactors, was designed and used sequentially and semi-continuously for biogas production. All effective operational parameters were controlled in both reactors over the course of the study. The results indicated that the organic matters were quickly decreased during the start-up phase in the first reactor, resulting in 52% and 64% reduction in total solids and total volatile solids, respectively, while the corresponding reductions in the methanogenic reactor were 39.7% and 51.4%. The production of hydrogen was observed during the first 20 d of digestion, where the maximum concentration of 76.5% was detected after 8 d when the pH stood at 5.96. After 21 d of digestion, hydrogen concentration was decreased to less than 4.5%, while methane content was increased leading to an accumulated biogas yield of over 300 mL per g of total volatile solids. The high concentration of hydrogen in biogas was possibly due to the improvement in the growth of acidogenic bacteria in response to maintaining pH at their optimum value, leading to a more efficient organic residues hydrolysis.