High rate mesophilic, thermophilic, and temperature phased anaerobic digestion of waste activated sludge: A pilot scale study

ABSTRACTThis study investigated the process of high-rate, high-temperature methanogenesis to enable very-high-volume loading during anaerobic digestion of waste-activated sludge. Reducing the hydraulic retention time (HRT) from 15 to 20 days in mesophilic digestion down to 3 days was achievable at a thermophilic temperature (55°C) with stable digester performance and methanogenic activity. A volatile solids (VS) destruction efficiency of 33 to 35% was achieved on waste-activated sludge, comparable to that obtained via mesophilic processes with low organic acid levels (<200 mg/liter chemical oxygen demand [COD]). Methane yield (VS basis) was 150 to 180 liters of CH4/kg of VSadded. According to 16S rRNA pyrotag sequencing and fluorescence in situ hybridization (FISH), the methanogenic community was dominated by members of theMethanosarcinaceae, which have a high level of metabolic capability, including acetoclastic and hydrogenotrophic methanogenesis. Loss of function at an HRT of 2 days was accompanied by a loss of the methanogens, according to pyrotag sequencing. The two acetate conversion pathways, namely, acetoclastic methanogenesis and syntrophic acetate oxidation, were quantified by stable carbon isotope ratio mass spectrometry. The results showed that the majority of methane was generated by nonacetoclastic pathways, both in the reactors and in off-line batch tests, confirming that syntrophic acetate oxidation is a key pathway at elevated temperatures. The proportion of methane due to acetate cleavage increased later in the batch, and it is likely that stable oxidation in the continuous reactor was maintained by application of the consistently low retention time.

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Pilot-scale study of enhanced anaerobic digestion of waste activated sludge by electrochemical and sodium hypochlorite combination pretreatment

International Biodeterioration & Biodegradation ◽

10.1016/j.ibiod.2016.04.001 ◽

2016 ◽

Vol 110 ◽

pp. 227-234 ◽

Cited By ~ 18

Author(s):

Haiping Yuan ◽

Bao Yu ◽

Peiwen Cheng ◽

Nanwen Zhu ◽

Changkai Yin ◽

...

Keyword(s):

Anaerobic Digestion ◽

Activated Sludge ◽

Sodium Hypochlorite ◽

Pilot Scale ◽

Waste Activated Sludge

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Pilot-Scale Demonstration of Two-Phase Anaerobic Digestion of Activated Sludge

Water Science & Technology ◽

10.2166/wst.1991.0569 ◽

1991 ◽

Vol 23 (7-9) ◽

pp. 1179-1188 ◽

Cited By ~ 56

Author(s):

Sam Ghosh

Keyword(s):

Anaerobic Digestion ◽

Organic Acids ◽

Activated Sludge ◽

Loading Rate ◽

Pilot Scale ◽

Full Scale ◽

High Rate ◽

Methane Fermentation ◽

Two Phase ◽

Fermentation Products

An innovative pilot-scale two-phase anaerobic digestion process was developed to stabilize concentrated (7-5%) activated sludge at a 12-day SRT and a loading rate of 5 kg VS/m3 d. The pilot system exhibited an unusually high VS reduction of 73%, an aggregated carbohydrate-protein-lipid reduction of 71%, and a methane yield of 0.3 m3/kg VS added. Optimum acidogenic fermentation producing 9500 mg/l of organic acids was achieved at an HRT of 3 days and a loading rate of 16 kg VS/m3.d or higher. Enhanced acidogenic hydrolysis and prehydrolysis of polymerics and nocardial residues eliminated digester foaming. Sulfate and nitrate reductions, and syntrophic methane fermentation occurred during acidogenic conversions. Acetogenesis and aceticlastic methane fermentation were predominant in the methane digester, which generated 93% of the system methane production. Contrary to literature reports, there was no inhibition of acetogens or methanogens at a high ammonia-N concentration of 2500 mg/l and pH 7.7. The acid and methane digesters could be started quickly. They were resilient to temperature drops and loading fluctuations. Acid fermentation of 8% of the plant's WAS and addition of the resulting fermentation products (enzymes, organic acids, etc.) to the full-scale high-rate digester increased VS reduction by 46% and eliminated severe foaming. Full-scale two-phase digestion of WAS is scheduled to start in 1990.

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High-Rate Anaerobic Digestion of Waste Activated Sludge by Integration of Electro-Fenton Process

Molecules ◽

10.3390/molecules25030626 ◽

2020 ◽

Vol 25 (3) ◽

pp. 626 ◽

Cited By ~ 1

Author(s):

Emna Feki ◽

Audrey Battimelli ◽

Sami Sayadi ◽

Abdelhafidh Dhouib ◽

Sonia Khoufi

Keyword(s):

Anaerobic Digestion ◽

Activated Sludge ◽

Volatile Fatty Acids ◽

Continuous Fermentation ◽

Removal Rate ◽

High Rate ◽

Organic Loading Rate ◽

Waste Activated Sludge ◽

Capillary Suction ◽

Biogas Yield

Anaerobic digestion (AD), being the most effective treatment method of waste activated sludge (WAS), allows for safe disposal. The present study deals with the electro-Fenton (EF) pretreatment for enhancing the WAS biogas potential with low-cost iron electrodes. The effect of pretreatment on the physicochemical characteristics of sludge was assessed. Following EF pretreatment, the pH, conductivity, soluble chemical oxygen demand (SCOD), and volatile fatty acids (VFA) increased to 7.5, 13.72 mS/cm, 4.1 g/L, and 925 mg/L, respectively. Capillary suction time (CST) analysis highlighted the dewaterability effect of EF on WAS, as demonstrated by the decrease in CST from 429 to 180 s following 30 min of pretreatment. Batch digestion assays presented an increase in the biogas yield to 0.135 L/g volatile solids (VS) after 60 min of EF pretreatment in comparison to raw sludge (0.08 L/g VS). Production of biogas was also found to improve during semi-continuous fermentation of EF-pretreated sludge conducted in a lab-scale reactor. In comparison to raw sludge, EF-pretreated sludge produced the highest biogas yield (0.81 L biogas/g VS) with a high COD removal rate, reaching 96.6% at an organic loading rate (OLR) of 2.5 g VS/L. d. Results revealed that the EF process could be an effective WAS disintegration method with maximum recovery of bioenergy during AD.

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