Effect of sludge retention time on the biological performance of anaerobic membrane bioreactors treating corn-to-ethanol thin stillage with high lipid content (original) (raw)
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Anaerobic digestion of long-chain fatty acids in UASB and expanded granular sludge bed reactors
Process Biochemistry, 1993
Solutions of sodium caprate and sodium lam-ate were digested in upj7ow anaerobic sludge bed (UASB) reactors inoculated with granular sludge and in expanded granular sludge bed (EGSB) reactors. UASB reactors are unsuitable if lipids contribute 50% or more to the COD of waste water: the gas production rate required to obtain sufficient mixing and contact cannot be achieved. At lipid loading rates exceeding 2-3 kg COD m-3 day-', total sludge wash-out occurred. At lower loading rates the system was unreliable, due to unpredictable sludge fi'otation. EGSB reactors do fulfil the requirements of mixing and contact. They accommodate space loading rates up to 30 kg COD m-j day-' during digestion of caprate or laurate as sole substrate, at COD removal eficiencies of 83-91%, and can be operated at hydraulic residence times of 2 h without any problems. Augmentation of granular sludge in lab-scale EGSB reactors was demonstrated. The new granules had excellent settling properties. Floating layerformation, as well as mixing characteristics in full-scale EGSB reactors require further research.
Separation and Purification Technology, 2015
In this study, the filtration performance of anaerobic membrane bioreactors when treating a high strength lipid rich wastewater, corn-to-ethanol thin stillage, is evaluated at different solids retention times (SRTs). Long chain fatty acid (LCFA) inhibition, observed at high SRTs, concomitantly occurred with floc deterioration and soluble microbial product release. On the other hand, accumulation of LCFA on the sludge modified its surface hydrophobicity. Remarkably, a lesser degree of fouling was observed at increased sludge hydrophobicity. Cake layer formation was found as the most important contributor to membrane filtration resistance, whereas chemical cleaning tests indicated a low degree of irreversible organic fouling. Moreover, inorganic fouling in the form of phosphorus precipitates was identified both in the cake layer and on the membrane.
Environmental Technology, 2019
In this study, the impact of applied solids retention time (SRT) on the biological performance of an anaerobic membrane bioreactor (AnMBR) treating synthetic dairy wastewater with high lipid content was assessed. Two side-stream AnMBR systems were operated at an SRT of 20 and 40 days (R20 and R40, respectively), equipped with an inside-out tubular membrane operated in cross-flow mode under full-scale operational conditions, i.e. crossflow velocity, transmembrane pressure, membrane flux. Successful operation was achieved and removal efficiencies of both reactors were up to 99% applying an organic loading rate (OLR) of 4.7 g COD L −1 d −1. No precipitation of lipids was observed throughout the operational period, keeping the lipids available for the anaerobic degradation. Long chain fatty acid (LCFA) accumulation was very modest and amounted 148 and 115 mg LCFA-COD per gram of volatile suspended solids (VSS) for R20 and R40, respectively. At an SRT of 40 days, a slightly better biological conversion was obtained. Periodically performed specific methanogenic activity (SMA) tests showed stabilization of the SMA for R40 sludge, whereas for R20 sludge the SMA continued to decrease. This study revealed a more stable reactor performance operating the AnMBR at an SRT of 40 days compared to 20 days.
2017
In this work, the performance of organic pollutant removal, membrane fouling and sludge morphology in a submerged membrane bioreactor (MBR) treating sunflower oil refinery wastewater (SORW) containing high oleic content was studied during 52 days’ operation at short values of 18 h and 10 days for hydraulic retention time and sludge retention time, respectively. The removal efficiencies of chemical oxygen demand (COD), oil and grease (O&G) and turbidity were found to be 73.2±6.6%, 75.1±2.5%, and 99.7±0.1%, respectively and the need for membrane cleaning never rose. The results showed a statistically significant linear correlation between the mixed liquor O&G with soluble microbial products and extracellular polymeric substances (EPS) (rP=0.792; p-value=0.034 and rP=0.920; p-value=0.003, respectively). Additionally, increase in MLVSS concentration which was due to an increase in cell concentration and was not related to accumulation of O&G and biopolymers inside the bioreactor, increa...
Water Research, 2005
This study investigated the performance and biomass characteristics of a membrane bioreactor (MBR) and a completely mixed activated sludge (CMAS) system operated at short solids retention times (SRT) ranging from 0.25 to 5 d and hydraulic retention times (HRT) of 3 and 6 h. The lab-scale reactors were fed with synthetic wastewater to ensure consistency in feed composition. For each experimental run, the reactors were inoculated with thawed activated sludge biomass previously frozen at-80 o C with 15% (v/v) glycerol. Results showed that at SRT of 0.25 d, the MBR effluent total chemical oxygen demand (TCOD) was 10.7 ± 4.4 mg/L, compared to TCOD of 90.0 ± 9.2 mg/L and soluble COD (SCOD) of 23.7 ± 2.9 mg/L for the CMAS. Removal efficiencies were approximately 97.3-98.4% (TCOD) in the MBR, compared to 77.5-93.8% (TCOD) and 94.1-97.0% (SCOD) in the CMAS. Nitrification completely ceased when SRT was < 2.5 d. The MBR biomass was composed of small, weak and uniform-sized flocs with large mass of short filamentous organisms and mainly dispersed microorganisms at SRT of 5 and 0.25 d, respectively. In contrast, the CMAS sludge was composed of large flocs with filamentous organisms as a backbone at SRT >2.5 d. The CMAS flocs were smaller and weaker at shorter SRT. Higher life forms were not observed in either system under any operating condition. The MBR sludge contained a much higher fraction of non-flocculating microorganisms. This fraction increased significantly with decreasing SRT. It was found that the concentrations of protein and carbohydrates in the exocellular polymeric substances (EPS) for both the MBR and the CMAS decreased with increasing F/M ratio or decreasing SRT. The combination of increasing amounts of non-flocculating microorganisms and a reduction of EPS at shorter SRT in both reactors contributed to deteriorating sludge settling properties. A significant presence of dispersed biomass and small flocs in MBR contributed to better reactor 2 performance probably due to less mass transfer resistance. The results showed that it is feasible to operate a MBR at extremely short solids retention time producing excellent effluent qualities in terms of organics removal and free of suspended solids.
BioResources
A two-stage submerged anaerobic membrane bioreactor (2-sAnMBR) was operated to demonstrate the technology concept and to accelerate anaerobic biodegradation of Palm Oil Mill Effluent (POME). Then, the impact of different high organic loading rates (OLR) was investigated with a focus on water quality and biogas production. OLR higher than 50 kgCOD.m-3.d-1 induced an increase of volatile fatty acids (VFAs). As a consequence, the biogas production decreased from 19.8 to 11.0 L.d-1 and CH4 yield between 0.23 to 0.38 LCH4/gCODremoved. Nevertheless, the highest OLR (98 kgCOD.m-3.d-1) made it possible to reach a COD removal effectiveness of 70%, where the membrane contribution was around 23.9% to 34.7%. The ratio of propionic acid/acetic acid appeared to be a key indicator to prevent the AnMBR operation failure. Indeed, as soon as the value of 0.7 has been exceeded, several signs of AnMBR failure appeared. The methanogenic activity in AnMBR was inhibited by a hydrolysis ratio of 13% which ...
Desalination, 2011
This study aimed at evaluating the effect of increasing organic loading rates and of enzyme pretreatment on the stability and efficiency of a hybrid upflow anaerobic sludge blanket reactor (UASBh) treating dairy effluent. The UASBh was submitted to the following average organic loading rates (OLR) 0.98 Kg.m −3 .d −1 , 4.58 Kg.m −3 .d −1 , 8.89 Kg.m −3 .d −1 and 15.73 Kg.m −3 .d −1 , and with the higher value, the reactor was fed with effluent with and without an enzymatic pretreatment to hydrolyze fats. The hydraulic detention time was 24 h, and the temperature was 30 ± 2°C. The reactor was equipped with a superior foam bed and showed good efficiency and stability until an OLR of 8.89 Kg.m −3 .d −1 . The foam bed was efficient for solid retention and residual volatile acid concentration consumption. The enzymatic pretreatment did not contribute to the process stability, propitiating loss in both biomass and system efficiency. Specific methanogenic activity tests indicated the presence of inhibition after the sludge had been submitted to the pretreated effluent. It was concluded that continuous exposure to the hydrolysis products or to the enzyme caused a dramatic drop in the efficiency and stability of the process, and the single exposure of the biomass to this condition did not inhibit methane formation.
2007
A mixture of skim milk and sodium oleate was fed to an upflow sludge bed reactor operated in cycles. Each cycle had a feeding phase under continuous operation and a reaction phase in batch. Five cycles were performed with organic loading rates applied during feeding phases varying between 4.4 and 8 kg COD.m-3 .d-1 and a constant hydraulic retention time of 1.6 days. In the first two cycles, 70% of the methane-COD was produced in the reaction batch phase, whereas from the third to the fifth cycles, biogas production in the reaction phase was less than 3% of total production. Overall methane yields increased steadily, from 0.67 to 0.91 kg COD-CH 4 .kg COD removed-1. LCFA accumulated into the sludge in the first two cycles, being palmitate and stearate the dominant intermediates quantified. In the subsequent cycles no LCFA were detected in the solid or liquid phases. The specific methanogenic activity in the presence of acetate and H 2 /CO 2 increased significantly along the operation, particularly between time zero and the end of the third cycle. These results show that a discontinuous operation promoted the development of an active anaerobic community able to efficiently convert a continuous organic load of 8.2 kg COD.m-3 .d-1 , from which 50% was oleate.
IESL Annual Sessions 2016, 2016
Anaerobic treatment processes have been extensively developed for the treatment of various wastewaters containing high concentrations of organic substrates including proteins, carbohydrates and lipids. The desiccated coconut industry in Sri Lanka is one of the industries where wastewater with high concentrations of lipids containing medium chain saturated fatty acids (~55%), long chain saturated fatty acids (~35%) and long chain unsaturated fatty acids (~10%) is generated. The long chain organic molecules of lipids undergo a series of complex biochemical reactions such as hydrolysis, acidogenesis, acetogenesis and methanogenesis during anaerobic digestion. According to previous studies, high concentrations of lipids have an inhibitory effect on anaerobic treatment processes, due to the mass transfer limitations and toxicity caused by long chain fatty acids (LCFA) towards syntrophic substrate-degrading bacteria. Undesirable effects of accumulation of LCFA in anaerobic reactors comprise of gradual drop down of rate of biogas production and derogatory effects on quality characteristics of effluents such as chemical oxygen demand (COD), biochemical oxygen demand (BOD) and oil and grease removal efficiencies after anaerobic treatment, causing the treatment process inefficient. According to the case study, desiccated coconut wastewater (DCWW) has pH 4.0 - 5.5, COD 4,000 mg/l - 8,000 mg/l, BOD 1,000 mg/l - 5,000 mg/l and total lipids 4,000 mg/l. In anaerobic treatment of DCWW, the COD removal efficiency rapidly changes from 90% - 30% due to the lipid inhibition caused by medium chain and LCFA in DCWW such as lauric acid and myristic acid. The treatment efficiency of anaerobic digestion can be enhanced via different physicochemical strategies.